diff --git a/flang/lib/Optimizer/Builder/Character.cpp b/flang/lib/Optimizer/Builder/Character.cpp
--- a/flang/lib/Optimizer/Builder/Character.cpp
+++ b/flang/lib/Optimizer/Builder/Character.cpp
@@ -422,7 +422,7 @@
       (lhsCstLen && rhsCstLen && *lhsCstLen == *rhsCstLen) ||
       (rhs.getLen() == lhs.getLen());
 
-  if (compileTimeSameLength && *lhsCstLen == 1) {
+  if (compileTimeSameLength && lhsCstLen && *lhsCstLen == 1) {
     createLengthOneAssign(lhs, rhs);
     return;
   }