diff --git a/crates/assists/src/handlers/convert_integer_literal.rs b/crates/assists/src/handlers/convert_integer_literal.rs
index ea35e833a94..c8af807012d 100644
--- a/crates/assists/src/handlers/convert_integer_literal.rs
+++ b/crates/assists/src/handlers/convert_integer_literal.rs
@@ -1,4 +1,4 @@
-use syntax::{ast, AstNode, SmolStr};
+use syntax::{ast, ast::Radix, AstNode};
 
 use crate::{AssistContext, AssistId, AssistKind, Assists, GroupLabel};
 
@@ -15,37 +15,34 @@ use crate::{AssistContext, AssistId, AssistKind, Assists, GroupLabel};
 // ```
 pub(crate) fn convert_integer_literal(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let literal = ctx.find_node_at_offset::<ast::Literal>()?;
+    let (radix, value) = literal.int_value()?;
+
     let range = literal.syntax().text_range();
     let group_id = GroupLabel("Convert integer base".into());
-
     let suffix = match literal.kind() {
         ast::LiteralKind::IntNumber { suffix } => suffix,
         _ => return None,
     };
-    let suffix_len = suffix.as_ref().map(|s| s.len()).unwrap_or(0);
-    let raw_literal_text = literal.syntax().to_string();
 
-    // Gets the literal's text without the type suffix and without underscores.
-    let literal_text = raw_literal_text
-        .chars()
-        .take(raw_literal_text.len() - suffix_len)
-        .filter(|c| *c != '_')
-        .collect::<SmolStr>();
-    let literal_base = IntegerLiteralBase::identify(&literal_text)?;
-
-    for base in IntegerLiteralBase::bases() {
-        if *base == literal_base {
+    for &target_radix in Radix::ALL {
+        if target_radix == radix {
             continue;
         }
 
-        let mut converted = literal_base.convert(&literal_text, base);
-
-        let label = if let Some(suffix) = &suffix {
-            format!("Convert {} ({}) to {}", &literal_text, suffix, &converted)
-        } else {
-            format!("Convert {} to {}", &literal_text, &converted)
+        let mut converted = match target_radix {
+            Radix::Binary => format!("0b{:b}", value),
+            Radix::Octal => format!("0o{:o}", value),
+            Radix::Decimal => value.to_string(),
+            Radix::Hexadecimal => format!("0x{:X}", value),
         };
 
+        let label = format!(
+            "Convert {} to {}{}",
+            literal,
+            converted,
+            suffix.as_deref().unwrap_or_default()
+        );
+
         // Appends the type suffix back into the new literal if it exists.
         if let Some(suffix) = &suffix {
             converted.push_str(&suffix);
@@ -63,79 +60,11 @@ pub(crate) fn convert_integer_literal(acc: &mut Assists, ctx: &AssistContext) ->
     Some(())
 }
 
-#[derive(Debug, PartialEq, Eq)]
-enum IntegerLiteralBase {
-    Binary,
-    Octal,
-    Decimal,
-    Hexadecimal,
-}
-
-impl IntegerLiteralBase {
-    fn identify(literal_text: &str) -> Option<Self> {
-        // We cannot express a literal in anything other than decimal in under 3 characters, so we return here if possible.
-        if literal_text.len() < 3 && literal_text.chars().all(|c| c.is_digit(10)) {
-            return Some(Self::Decimal);
-        }
-
-        let base = match &literal_text[..2] {
-            "0b" => Self::Binary,
-            "0o" => Self::Octal,
-            "0x" => Self::Hexadecimal,
-            _ => Self::Decimal,
-        };
-
-        // Checks that all characters after the base prefix are all valid digits for that base.
-        if literal_text[base.prefix_len()..].chars().all(|c| c.is_digit(base.base())) {
-            Some(base)
-        } else {
-            None
-        }
-    }
-
-    fn convert(&self, literal_text: &str, to: &IntegerLiteralBase) -> String {
-        let digits = &literal_text[self.prefix_len()..];
-        let value = u128::from_str_radix(digits, self.base()).unwrap();
-
-        match to {
-            Self::Binary => format!("0b{:b}", value),
-            Self::Octal => format!("0o{:o}", value),
-            Self::Decimal => value.to_string(),
-            Self::Hexadecimal => format!("0x{:X}", value),
-        }
-    }
-
-    const fn base(&self) -> u32 {
-        match self {
-            Self::Binary => 2,
-            Self::Octal => 8,
-            Self::Decimal => 10,
-            Self::Hexadecimal => 16,
-        }
-    }
-
-    const fn prefix_len(&self) -> usize {
-        match self {
-            Self::Decimal => 0,
-            _ => 2,
-        }
-    }
-
-    const fn bases() -> &'static [IntegerLiteralBase] {
-        &[
-            IntegerLiteralBase::Binary,
-            IntegerLiteralBase::Octal,
-            IntegerLiteralBase::Decimal,
-            IntegerLiteralBase::Hexadecimal,
-        ]
-    }
-}
-
 #[cfg(test)]
 mod tests {
+    use crate::tests::{check_assist_by_label, check_assist_not_applicable, check_assist_target};
 
     use super::*;
-    use crate::tests::{check_assist_by_label, check_assist_target};
 
     #[test]
     fn binary_target() {
@@ -317,21 +246,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b1111101000;",
-            "Convert 1000 to 0b1111101000",
+            "Convert 1_00_0 to 0b1111101000",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o1750;",
-            "Convert 1000 to 0o1750",
+            "Convert 1_00_0 to 0o1750",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0x3E8;",
-            "Convert 1000 to 0x3E8",
+            "Convert 1_00_0 to 0x3E8",
         );
     }
 
@@ -343,21 +272,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b1010;",
-            "Convert 10 to 0b1010",
+            "Convert 1_0 to 0b1010",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o12;",
-            "Convert 10 to 0o12",
+            "Convert 1_0 to 0o12",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xA;",
-            "Convert 10 to 0xA",
+            "Convert 1_0 to 0xA",
         );
     }
 
@@ -369,21 +298,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b11111111;",
-            "Convert 0xFF to 0b11111111",
+            "Convert 0x_F_F to 0b11111111",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o377;",
-            "Convert 0xFF to 0o377",
+            "Convert 0x_F_F to 0o377",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255;",
-            "Convert 0xFF to 255",
+            "Convert 0x_F_F to 255",
         );
     }
 
@@ -395,21 +324,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0o377;",
-            "Convert 0b11111111 to 0o377",
+            "Convert 0b1111_1111 to 0o377",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255;",
-            "Convert 0b11111111 to 255",
+            "Convert 0b1111_1111 to 255",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xFF;",
-            "Convert 0b11111111 to 0xFF",
+            "Convert 0b1111_1111 to 0xFF",
         );
     }
 
@@ -421,21 +350,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b11111111;",
-            "Convert 0o377 to 0b11111111",
+            "Convert 0o3_77 to 0b11111111",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255;",
-            "Convert 0o377 to 255",
+            "Convert 0o3_77 to 255",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xFF;",
-            "Convert 0o377 to 0xFF",
+            "Convert 0o3_77 to 0xFF",
         );
     }
 
@@ -447,21 +376,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b1111101000i32;",
-            "Convert 1000 (i32) to 0b1111101000",
+            "Convert 1000i32 to 0b1111101000i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o1750i32;",
-            "Convert 1000 (i32) to 0o1750",
+            "Convert 1000i32 to 0o1750i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0x3E8i32;",
-            "Convert 1000 (i32) to 0x3E8",
+            "Convert 1000i32 to 0x3E8i32",
         );
     }
 
@@ -473,21 +402,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b1010i32;",
-            "Convert 10 (i32) to 0b1010",
+            "Convert 10i32 to 0b1010i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o12i32;",
-            "Convert 10 (i32) to 0o12",
+            "Convert 10i32 to 0o12i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xAi32;",
-            "Convert 10 (i32) to 0xA",
+            "Convert 10i32 to 0xAi32",
         );
     }
 
@@ -499,21 +428,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b11111111i32;",
-            "Convert 0xFF (i32) to 0b11111111",
+            "Convert 0xFFi32 to 0b11111111i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o377i32;",
-            "Convert 0xFF (i32) to 0o377",
+            "Convert 0xFFi32 to 0o377i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255i32;",
-            "Convert 0xFF (i32) to 255",
+            "Convert 0xFFi32 to 255i32",
         );
     }
 
@@ -525,21 +454,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0o377i32;",
-            "Convert 0b11111111 (i32) to 0o377",
+            "Convert 0b11111111i32 to 0o377i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255i32;",
-            "Convert 0b11111111 (i32) to 255",
+            "Convert 0b11111111i32 to 255i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xFFi32;",
-            "Convert 0b11111111 (i32) to 0xFF",
+            "Convert 0b11111111i32 to 0xFFi32",
         );
     }
 
@@ -551,21 +480,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b11111111i32;",
-            "Convert 0o377 (i32) to 0b11111111",
+            "Convert 0o377i32 to 0b11111111i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255i32;",
-            "Convert 0o377 (i32) to 255",
+            "Convert 0o377i32 to 255i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xFFi32;",
-            "Convert 0o377 (i32) to 0xFF",
+            "Convert 0o377i32 to 0xFFi32",
         );
     }
 
@@ -577,21 +506,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b1111101000i32;",
-            "Convert 1000 (i32) to 0b1111101000",
+            "Convert 1_00_0i32 to 0b1111101000i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o1750i32;",
-            "Convert 1000 (i32) to 0o1750",
+            "Convert 1_00_0i32 to 0o1750i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0x3E8i32;",
-            "Convert 1000 (i32) to 0x3E8",
+            "Convert 1_00_0i32 to 0x3E8i32",
         );
     }
 
@@ -603,21 +532,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b1010i32;",
-            "Convert 10 (i32) to 0b1010",
+            "Convert 1_0i32 to 0b1010i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o12i32;",
-            "Convert 10 (i32) to 0o12",
+            "Convert 1_0i32 to 0o12i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xAi32;",
-            "Convert 10 (i32) to 0xA",
+            "Convert 1_0i32 to 0xAi32",
         );
     }
 
@@ -629,21 +558,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b11111111i32;",
-            "Convert 0xFF (i32) to 0b11111111",
+            "Convert 0x_F_Fi32 to 0b11111111i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0o377i32;",
-            "Convert 0xFF (i32) to 0o377",
+            "Convert 0x_F_Fi32 to 0o377i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255i32;",
-            "Convert 0xFF (i32) to 255",
+            "Convert 0x_F_Fi32 to 255i32",
         );
     }
 
@@ -655,21 +584,21 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0o377i32;",
-            "Convert 0b11111111 (i32) to 0o377",
+            "Convert 0b1111_1111i32 to 0o377i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255i32;",
-            "Convert 0b11111111 (i32) to 255",
+            "Convert 0b1111_1111i32 to 255i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xFFi32;",
-            "Convert 0b11111111 (i32) to 0xFF",
+            "Convert 0b1111_1111i32 to 0xFFi32",
         );
     }
 
@@ -681,21 +610,28 @@ mod tests {
             convert_integer_literal,
             before,
             "const _: i32 = 0b11111111i32;",
-            "Convert 0o377 (i32) to 0b11111111",
+            "Convert 0o3_77i32 to 0b11111111i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 255i32;",
-            "Convert 0o377 (i32) to 255",
+            "Convert 0o3_77i32 to 255i32",
         );
 
         check_assist_by_label(
             convert_integer_literal,
             before,
             "const _: i32 = 0xFFi32;",
-            "Convert 0o377 (i32) to 0xFF",
+            "Convert 0o3_77i32 to 0xFFi32",
         );
     }
+
+    #[test]
+    fn convert_overflowing_literal() {
+        let before = "const _: i32 =
+            111111111111111111111111111111111111111111111111111111111111111111111111<|>;";
+        check_assist_not_applicable(convert_integer_literal, before);
+    }
 }
diff --git a/crates/syntax/src/ast.rs b/crates/syntax/src/ast.rs
index 8a0e3d27b21..a16ac6a7c90 100644
--- a/crates/syntax/src/ast.rs
+++ b/crates/syntax/src/ast.rs
@@ -16,7 +16,7 @@ use crate::{
 };
 
 pub use self::{
-    expr_ext::{ArrayExprKind, BinOp, Effect, ElseBranch, LiteralKind, PrefixOp, RangeOp},
+    expr_ext::{ArrayExprKind, BinOp, Effect, ElseBranch, LiteralKind, PrefixOp, Radix, RangeOp},
     generated::{nodes::*, tokens::*},
     node_ext::{
         AttrKind, FieldKind, NameOrNameRef, PathSegmentKind, SelfParamKind, SlicePatComponents,
diff --git a/crates/syntax/src/ast/expr_ext.rs b/crates/syntax/src/ast/expr_ext.rs
index f5ba872233f..3aff01e837a 100644
--- a/crates/syntax/src/ast/expr_ext.rs
+++ b/crates/syntax/src/ast/expr_ext.rs
@@ -358,6 +358,71 @@ impl ast::Literal {
             _ => unreachable!(),
         }
     }
+
+    // FIXME: should probably introduce string token type?
+    // https://github.com/rust-analyzer/rust-analyzer/issues/6308
+    pub fn int_value(&self) -> Option<(Radix, u128)> {
+        let suffix = match self.kind() {
+            LiteralKind::IntNumber { suffix } => suffix,
+            _ => return None,
+        };
+
+        let token = self.token();
+        let mut text = token.text().as_str();
+        text = &text[..text.len() - suffix.map_or(0, |it| it.len())];
+
+        let buf;
+        if text.contains("_") {
+            buf = text.replace('_', "");
+            text = buf.as_str();
+        };
+
+        let radix = Radix::identify(text)?;
+        let digits = &text[radix.prefix_len()..];
+        let value = u128::from_str_radix(digits, radix as u32).ok()?;
+        Some((radix, value))
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub enum Radix {
+    Binary = 2,
+    Octal = 8,
+    Decimal = 10,
+    Hexadecimal = 16,
+}
+
+impl Radix {
+    pub const ALL: &'static [Radix] =
+        &[Radix::Binary, Radix::Octal, Radix::Decimal, Radix::Hexadecimal];
+
+    fn identify(literal_text: &str) -> Option<Self> {
+        // We cannot express a literal in anything other than decimal in under 3 characters, so we return here if possible.
+        if literal_text.len() < 3 && literal_text.chars().all(|c| c.is_digit(10)) {
+            return Some(Self::Decimal);
+        }
+
+        let res = match &literal_text[..2] {
+            "0b" => Radix::Binary,
+            "0o" => Radix::Octal,
+            "0x" => Radix::Hexadecimal,
+            _ => Radix::Decimal,
+        };
+
+        // Checks that all characters after the base prefix are all valid digits for that base.
+        if literal_text[res.prefix_len()..].chars().all(|c| c.is_digit(res as u32)) {
+            Some(res)
+        } else {
+            None
+        }
+    }
+
+    const fn prefix_len(&self) -> usize {
+        match self {
+            Self::Decimal => 0,
+            _ => 2,
+        }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]