Index: lib/Support/SpecialCaseList.cpp
===================================================================
--- lib/Support/SpecialCaseList.cpp
+++ lib/Support/SpecialCaseList.cpp
@@ -28,6 +28,11 @@
 
 bool SpecialCaseList::Matcher::insert(std::string Regexp,
                                       std::string &REError) {
+  if (Regexp.empty()) {
+    REError = "Supplied regexp was blank";
+    return false;
+  }
+
   if (Regex::isLiteralERE(Regexp)) {
     Strings.insert(Regexp);
     return true;