diff --git a/clippy_lints/src/functions.rs b/clippy_lints/src/functions.rs
index 789660391a4..eadbd01e4ea 100644
--- a/clippy_lints/src/functions.rs
+++ b/clippy_lints/src/functions.rs
@@ -4,6 +4,7 @@ use rustc::ty;
 use rustc::lint::*;
 use std::collections::HashSet;
 use syntax::ast;
+use syntax::abi::Abi;
 use syntax::codemap::Span;
 use utils::{span_lint, type_is_unsafe_function};
 
@@ -85,7 +86,12 @@ impl LateLintPass for Functions {
 
         // don't warn for implementations, it's not their fault
         if !is_impl {
-            self.check_arg_number(cx, decl, span);
+            // don't lint extern functions decls, it's not their fault either
+            match kind {
+                hir::intravisit::FnKind::Method(_, &hir::MethodSig { abi: Abi::Rust, .. }, _, _) |
+                hir::intravisit::FnKind::ItemFn(_, _, _, _, Abi::Rust, _, _) => self.check_arg_number(cx, decl, span),
+                _ => {},
+            }
         }
 
         self.check_raw_ptr(cx, unsafety, decl, block, nodeid);
@@ -93,7 +99,10 @@ impl LateLintPass for Functions {
 
     fn check_trait_item(&mut self, cx: &LateContext, item: &hir::TraitItem) {
         if let hir::MethodTraitItem(ref sig, ref block) = item.node {
-            self.check_arg_number(cx, &sig.decl, item.span);
+            // don't lint extern functions decls, it's not their fault
+            if sig.abi == Abi::Rust {
+                self.check_arg_number(cx, &sig.decl, item.span);
+            }
 
             if let Some(ref block) = *block {
                 self.check_raw_ptr(cx, sig.unsafety, &sig.decl, block, item.id);
diff --git a/tests/compile-fail/functions.rs b/tests/compile-fail/functions.rs
index f7ee41d2816..60a074df0f5 100644
--- a/tests/compile-fail/functions.rs
+++ b/tests/compile-fail/functions.rs
@@ -12,6 +12,9 @@ fn bad(_one: u32, _two: u32, _three: &str, _four: bool, _five: f32, _six: f32, _
     //~^ ERROR: this function has too many arguments (8/7)
 }
 
+// don't lint extern fns
+extern fn extern_fn(_one: u32, _two: u32, _three: &str, _four: bool, _five: f32, _six: f32, _seven: bool, _eight: ()) {}
+
 pub trait Foo {
     fn good(_one: u32, _two: u32, _three: &str, _four: bool, _five: f32, _six: f32, _seven: bool);
     fn bad(_one: u32, _two: u32, _three: &str, _four: bool, _five: f32, _six: f32, _seven: bool, _eight: ());