diff --git a/quiche/common/balsa/header_properties.cc b/quiche/common/balsa/header_properties.cc
index 415bc4d..6722239 100644
--- a/quiche/common/balsa/header_properties.cc
+++ b/quiche/common/balsa/header_properties.cc
@@ -62,7 +62,7 @@
 std::array<bool, 256> buildInvalidCharLookupTable() {
   std::array<bool, 256> invalidCharTable;
   invalidCharTable.fill(false);
-  for (char c : kInvalidHeaderCharList) {
+  for (uint8_t c : kInvalidHeaderCharList) {
     invalidCharTable[c] = true;
   }
   return invalidCharTable;
@@ -76,7 +76,7 @@
   return multivalued_headers->contains(header);
 }
 
-bool IsInvalidHeaderChar(char c) {
+bool IsInvalidHeaderChar(uint8_t c) {
   static const std::array<bool, 256> invalidCharTable =
       buildInvalidCharLookupTable();
 
diff --git a/quiche/common/balsa/header_properties.h b/quiche/common/balsa/header_properties.h
index a747fab..6b43763 100644
--- a/quiche/common/balsa/header_properties.h
+++ b/quiche/common/balsa/header_properties.h
@@ -5,6 +5,8 @@
 #ifndef QUICHE_COMMON_BALSA_HEADER_PROPERTIES_H_
 #define QUICHE_COMMON_BALSA_HEADER_PROPERTIES_H_
 
+#include <cstdint>
+
 #include "absl/strings/string_view.h"
 #include "quiche/common/platform/api/quiche_export.h"
 
@@ -27,7 +29,7 @@
 
 // Returns true if the given `c` is invalid in a header field or the `value` has
 // invalid characters.
-QUICHE_EXPORT_PRIVATE bool IsInvalidHeaderChar(char c);
+QUICHE_EXPORT_PRIVATE bool IsInvalidHeaderChar(uint8_t c);
 QUICHE_EXPORT_PRIVATE bool HasInvalidHeaderChars(absl::string_view value);
 
 }  // namespace quiche::header_properties