--- a/build/moz.configure/warnings.configure
+++ b/build/moz.configure/warnings.configure
@@ -37,16 +37,17 @@ add_gcc_warning('-Wpointer-arith')
 # catches comparing signed/unsigned ints
 add_gcc_warning('-Wsign-compare')
 
 # catches overflow bugs, few false positives
 add_gcc_warning('-Wtype-limits')
 
 # catches some dead code
 add_gcc_warning('-Wunreachable-code')
+check_and_add_gcc_warning('-Wunreachable-code-return')
 
 # catches treating string literals as non-const
 add_gcc_warning('-Wwrite-strings', cxx_compiler)
 
 # turned on by -Wall, but we use offsetof on non-POD types frequently
 add_gcc_warning('-Wno-invalid-offsetof', cxx_compiler)
 
 # catches objects passed by value to variadic functions.