diff --git a/lib/Frontend/TextDiagnostic.cpp b/lib/Frontend/TextDiagnostic.cpp
index 6636238..65fb1ae 100644
--- a/lib/Frontend/TextDiagnostic.cpp
+++ b/lib/Frontend/TextDiagnostic.cpp
@@ -114,6 +114,7 @@
 
     ConversionResult res = ConvertUTF8toUTF32(&begin, cp_end, &cptr, cptr+1,
                                               strictConversion);
+    (void)res;
     assert(conversionOK==res);
     assert(0 < begin-original_begin
            && "we must be further along in the string now");
@@ -1161,4 +1162,3 @@
     OS << "\"\n";
   }
 }
-