1 files changed, 5 insertions, 1 deletions
diff --git a/llvm/utils/FileCheck/FileCheck.cpp b/llvm/utils/FileCheck/FileCheck.cpp
index 46821ec..3f7d777 100644
--- a/llvm/utils/FileCheck/FileCheck.cpp
+++ b/llvm/utils/FileCheck/FileCheck.cpp
@@ -601,8 +601,12 @@ int main(int argc, char **argv) {
     Req.Verbose = true;
 
   FileCheck FC(Req);
-  if (!FC.ValidateCheckPrefixes())
+  if (!FC.ValidateCheckPrefixes()) {
+    errs() << "Supplied check-prefix is invalid! Prefixes must be unique and "
+              "start with a letter and contain only alphanumeric characters, "
+              "hyphens and underscores\n";
     return 2;
+  }
 
   Regex PrefixRE = FC.buildCheckPrefixRegex();
   std::string REError;