diff --git a/flang/runtime/character.cpp b/flang/runtime/character.cpp
--- a/flang/runtime/character.cpp
+++ b/flang/runtime/character.cpp
@@ -20,11 +20,13 @@
 
 template <typename CHAR>
 inline int CompareToBlankPadding(const CHAR *x, std::size_t chars) {
+  using UNSIGNED_CHAR = std::make_unsigned_t<CHAR>;
+  const auto blank{static_cast<UNSIGNED_CHAR>(' ')};
   for (; chars-- > 0; ++x) {
-    if (*x < ' ') {
+    if (*reinterpret_cast<const UNSIGNED_CHAR *>(x) < blank) {
       return -1;
     }
-    if (*x > ' ') {
+    if (*reinterpret_cast<const UNSIGNED_CHAR *>(x) > blank) {
       return 1;
     }
   }
diff --git a/flang/unittests/Runtime/CharacterTest.cpp b/flang/unittests/Runtime/CharacterTest.cpp
--- a/flang/unittests/Runtime/CharacterTest.cpp
+++ b/flang/unittests/Runtime/CharacterTest.cpp
@@ -171,6 +171,8 @@
         std::make_tuple("abc", "def", 3, 3, -1),
         std::make_tuple("ab ", "abc", 3, 2, 0),
         std::make_tuple("abc", "abc", 2, 3, -1),
+        std::make_tuple("ab\xff", "ab ", 3, 2, 1),
+        std::make_tuple("ab ", "ab\xff", 2, 3, -1),
     },
     {
         std::make_tuple(u"abc", u"abc", 3, 3, 0),