diff --git a/flang/runtime/format.h b/flang/runtime/format.h
--- a/flang/runtime/format.h
+++ b/flang/runtime/format.h
@@ -124,8 +124,13 @@
   CharType GetNextChar(IoErrorHandler &handler) {
     SkipBlanks();
     if (offset_ >= formatLength_) {
-      handler.SignalError(
-          IostatErrorInFormat, "FORMAT missing at least one ')'");
+      if (formatLength_ == 0) {
+        handler.SignalError(
+            IostatErrorInFormat, "Empty or badly assigned FORMAT");
+      } else {
+        handler.SignalError(
+            IostatErrorInFormat, "FORMAT missing at least one ')'");
+      }
       return '\n';
     }
     return format_[offset_++];