diff --git a/flang/lib/Evaluate/fold-integer.cpp b/flang/lib/Evaluate/fold-integer.cpp
--- a/flang/lib/Evaluate/fold-integer.cpp
+++ b/flang/lib/Evaluate/fold-integer.cpp
@@ -677,7 +677,11 @@
       return std::visit(
           [&](auto &kx) {
             if (auto len{kx.LEN()}) {
-              return Fold(context, ConvertToType<T>(*std::move(len)));
+              if (IsConstantExpr(len)) {
+                return Fold(context, ConvertToType<T>(*std::move(len)));
+              } else {
+                return Expr<T>{std::move(funcRef)};
+              }
             } else {
               return Expr<T>{std::move(funcRef)};
             }
diff --git a/flang/test/Evaluate/rewrite01.f90 b/flang/test/Evaluate/rewrite01.f90
--- a/flang/test/Evaluate/rewrite01.f90
+++ b/flang/test/Evaluate/rewrite01.f90
@@ -76,4 +76,33 @@
   !CHECK: PRINT *, 1_4
   print *, lbound(returns_array_3(), dim=1)
 end subroutine
+
+subroutine len_test(a,b, c, d)
+  character(*) :: a, b
+  external b
+  character(10) :: c, d
+  external d
+
+  !CHECK: PRINT *, len(a)
+  print *, len(a)
+  !CHECK: PRINT *, 5_4
+  print *, len(a(1:5))
+  !CHECK: PRINT *, len(b(a))
+  print *, len(b(a))
+  !CHECK: PRINT *, len(b(a)//a)
+  print *, len(b(a) // a)
+  !CHECK: PRINT *, 10_4
+  print *, len(c)
+  !CHECK: PRINT *, len(c(int(i,kind=8):int(j,kind=8)))
+  print *, len(c(i:j))
+  !CHECK: PRINT *, 5_4
+  print *, len(c(1:5))
+  !CHECK: PRINT *, 10_4
+  print *, len(d(c))
+  !CHECK: PRINT *, 20_4
+  print *, len(d(c) // c)
+  !CHECK: PRINT *, 0_4
+  print *, len(a(10:4))
+end subroutine len_test
+
 end module