diff --git a/lib/AsmParser/Lexer.l b/lib/AsmParser/Lexer.l
index e9996b28295..b4910ec5172 100644
--- a/lib/AsmParser/Lexer.l
+++ b/lib/AsmParser/Lexer.l
@@ -111,7 +111,7 @@ NInteger  -[0-9]+
 
 /* FPConstant - A Floating point constant.
    TODO: Expand lexer to support 10e50 FP constant notation */
-FPConstant [0-9]+[.][0-9]*
+FPConstant -?[0-9]+[.][0-9]*
 
 %%