diff --git a/lib/Support/Regex.cpp b/lib/Support/Regex.cpp
index dec967e33f5..54136418407 100644
--- a/lib/Support/Regex.cpp
+++ b/lib/Support/Regex.cpp
@@ -43,7 +43,7 @@ bool Regex::isValid(std::string &Error) {
   
   size_t len = llvm_regerror(error, preg, NULL, 0);
   
-  Error.resize(len);
+  Error.resize(len - 1);
   llvm_regerror(error, preg, &Error[0], len);
   return false;
 }
diff --git a/unittests/Support/RegexTest.cpp b/unittests/Support/RegexTest.cpp
index 02869b3ed46..7b977f74466 100644
--- a/unittests/Support/RegexTest.cpp
+++ b/unittests/Support/RegexTest.cpp
@@ -127,4 +127,12 @@ TEST_F(RegexTest, IsLiteralERE) {
   EXPECT_FALSE(Regex::isLiteralERE("abc{1,2}"));
 }
 
+TEST_F(RegexTest, IsValid) {
+  std::string Error;
+  EXPECT_FALSE(Regex("(foo").isValid(Error));
+  EXPECT_EQ("parentheses not balanced", Error);
+  EXPECT_FALSE(Regex("a[b-").isValid(Error));
+  EXPECT_EQ("invalid character range", Error);
+}
+
 }