1 files changed, 4 insertions, 1 deletions
diff --git a/clang/lib/Basic/Diagnostic.cpp b/clang/lib/Basic/Diagnostic.cpp
index 1f4316af3ff..7529c475d6b 100644
--- a/clang/lib/Basic/Diagnostic.cpp
+++ b/clang/lib/Basic/Diagnostic.cpp
@@ -742,7 +742,10 @@ FormatDiagnostic(const char *DiagStr, const char *DiagEnd,
         //   "%diff{compare $ to $|other text}1,2"
         // treat it as:
         //   "compare %1 to %2"
-        const char *Pipe = ScanFormat(Argument, Argument + ArgumentLen, '|');
+        const char *ArgumentEnd = Argument + ArgumentLen;
+        const char *Pipe = ScanFormat(Argument, ArgumentEnd, '|');
+        assert(ScanFormat(Pipe + 1, ArgumentEnd, '|') == ArgumentEnd &&
+               "Found too many '|'s in a %diff modifier!");
         const char *FirstDollar = ScanFormat(Argument, Pipe, '$');
         const char *SecondDollar = ScanFormat(FirstDollar + 1, Pipe, '$');
         const char ArgStr1[] = { '%', static_cast<char>('0' + ArgNo) };