diff --git a/mk/crates.mk b/mk/crates.mk
index bfd054ae988..cf3e479ec21 100644
--- a/mk/crates.mk
+++ b/mk/crates.mk
@@ -59,7 +59,7 @@ RUSTC_CRATES := rustc rustc_typeck rustc_mir rustc_borrowck rustc_resolve rustc_
                 rustc_data_structures rustc_front rustc_platform_intrinsics \
                 rustc_plugin rustc_metadata rustc_passes
 HOST_CRATES := syntax syntax_ext $(RUSTC_CRATES) rustdoc fmt_macros
-TOOLS := compiletest rustdoc rustc rustbook error-index-generator
+TOOLS := compiletest rustdoc rustc rustbook error_index_generator
 
 DEPS_core :=
 DEPS_alloc := core libc alloc_system
@@ -120,12 +120,12 @@ TOOL_DEPS_compiletest := test getopts
 TOOL_DEPS_rustdoc := rustdoc
 TOOL_DEPS_rustc := rustc_driver
 TOOL_DEPS_rustbook := std rustdoc
-TOOL_DEPS_error-index-generator := rustdoc syntax serialize
+TOOL_DEPS_error_index_generator := rustdoc syntax serialize
 TOOL_SOURCE_compiletest := $(S)src/compiletest/compiletest.rs
 TOOL_SOURCE_rustdoc := $(S)src/driver/driver.rs
 TOOL_SOURCE_rustc := $(S)src/driver/driver.rs
 TOOL_SOURCE_rustbook := $(S)src/rustbook/main.rs
-TOOL_SOURCE_error-index-generator := $(S)src/error-index-generator/main.rs
+TOOL_SOURCE_error_index_generator := $(S)src/error_index_generator/main.rs
 
 ONLY_RLIB_core := 1
 ONLY_RLIB_libc := 1
diff --git a/mk/dist.mk b/mk/dist.mk
index 685fb2b5b46..31d3764eefa 100644
--- a/mk/dist.mk
+++ b/mk/dist.mk
@@ -52,7 +52,7 @@ PKG_FILES := \
       doc                                      \
       driver                                   \
       etc                                      \
-      error-index-generator                    \
+      error_index_generator                    \
       $(foreach crate,$(CRATES),lib$(crate))   \
       libcollectionstest                       \
       libcoretest                              \
diff --git a/mk/docs.mk b/mk/docs.mk
index 7f73b99863f..83cdb7f8023 100644
--- a/mk/docs.mk
+++ b/mk/docs.mk
@@ -59,8 +59,8 @@ RUSTBOOK_EXE = $(HBIN2_H_$(CFG_BUILD))/rustbook$(X_$(CFG_BUILD))
 # ./configure
 RUSTBOOK = $(RPATH_VAR2_T_$(CFG_BUILD)_H_$(CFG_BUILD)) $(RUSTBOOK_EXE)
 
-# The error-index-generator executable...
-ERR_IDX_GEN_EXE = $(HBIN2_H_$(CFG_BUILD))/error-index-generator$(X_$(CFG_BUILD))
+# The error_index_generator executable...
+ERR_IDX_GEN_EXE = $(HBIN2_H_$(CFG_BUILD))/error_index_generator$(X_$(CFG_BUILD))
 ERR_IDX_GEN = $(RPATH_VAR2_T_$(CFG_BUILD)_H_$(CFG_BUILD)) $(ERR_IDX_GEN_EXE)
 ERR_IDX_GEN_MD = $(RPATH_VAR2_T_$(CFG_BUILD)_H_$(CFG_BUILD)) $(ERR_IDX_GEN_EXE) markdown
 
@@ -221,9 +221,9 @@ error-index: doc/error-index.html
 # Metadata used to generate the index is created as a side effect of
 # the build so this depends on every crate being up to date.
 doc/error-index.html: $(ERR_IDX_GEN_EXE) $(CSREQ$(2)_T_$(CFG_BUILD)_H_$(CFG_BUILD)) | doc/
-	$(Q)$(call E, error-index-generator: $@)
+	$(Q)$(call E, error_index_generator: $@)
 	$(Q)$(ERR_IDX_GEN)
 
 doc/error-index.md: $(ERR_IDX_GEN_EXE) $(CSREQ$(2)_T_$(CFG_BUILD)_H_$(CFG_BUILD)) | doc/
-	$(Q)$(call E, error-index-generator: $@)
+	$(Q)$(call E, error_index_generator: $@)
 	$(Q)$(ERR_IDX_GEN_MD)
diff --git a/mk/prepare.mk b/mk/prepare.mk
index 87a445000ad..2488de4ad5b 100644
--- a/mk/prepare.mk
+++ b/mk/prepare.mk
@@ -82,7 +82,7 @@ define PREPARE_MAN
 
 endef
 
-PREPARE_TOOLS = $(filter-out compiletest rustbook error-index-generator, $(TOOLS))
+PREPARE_TOOLS = $(filter-out compiletest rustbook error_index_generator, $(TOOLS))
 
 
 # $(1) is tool
diff --git a/src/error-index-generator/main.rs b/src/error_index_generator/main.rs
similarity index 100%
rename from src/error-index-generator/main.rs
rename to src/error_index_generator/main.rs
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index c96713a7285..28422989ea1 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -28,6 +28,7 @@ use syntax::attr;
 use syntax::attr::AttrMetaMethods;
 use syntax::errors::{ColorConfig, Handler};
 use syntax::parse;
+use syntax::parse::lexer::Reader;
 use syntax::parse::token::InternedString;
 use syntax::feature_gate::UnstableFeatures;
 
@@ -906,10 +907,19 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
 // Convert strings provided as --cfg [cfgspec] into a crate_cfg
 pub fn parse_cfgspecs(cfgspecs: Vec<String> ) -> ast::CrateConfig {
     cfgspecs.into_iter().map(|s| {
-        parse::parse_meta_from_source_str("cfgspec".to_string(),
-                                          s.to_string(),
-                                          Vec::new(),
-                                          &parse::ParseSess::new())
+        let sess = parse::ParseSess::new();
+        let mut parser = parse::new_parser_from_source_str(&sess,
+                                                           Vec::new(),
+                                                           "cfgspec".to_string(),
+                                                           s.to_string());
+        let meta_item = panictry!(parser.parse_meta_item());
+
+        if !parser.reader.is_eof() {
+            early_error(ErrorOutputType::default(), &format!("invalid --cfg argument: {}",
+                                                             s))
+        }
+
+        meta_item
     }).collect::<ast::CrateConfig>()
 }
 
diff --git a/src/test/compile-fail/cfg-arg-invalid.rs b/src/test/compile-fail/cfg-arg-invalid.rs
new file mode 100644
index 00000000000..404630399c6
--- /dev/null
+++ b/src/test/compile-fail/cfg-arg-invalid.rs
@@ -0,0 +1,13 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: --cfg a{b}
+// error-pattern: invalid --cfg argument: a{b}
+fn main() {}