diff --git a/quiche/balsa/header_properties.cc b/quiche/balsa/header_properties.cc
index 57ffbc10e..2f2aecdcc 100644
--- a/quiche/balsa/header_properties.cc
+++ b/quiche/balsa/header_properties.cc
@@ -241,7 +241,7 @@ bool HasInvalidHeaderChars(absl::string_view value) {
 bool HasInvalidPathChar(absl::string_view value) {
   static constexpr std::array<bool, 256> invalidCharTable =
       buildInvalidPathCharLookupTable();
-  for (const char c : value) {
+  for (const uint8_t c : value) {
     if (invalidCharTable[c]) {
       return true;
     }
@@ -252,7 +252,7 @@ bool HasInvalidPathChar(absl::string_view value) {
 bool HasInvalidQueryChar(absl::string_view value) {
   static constexpr std::array<bool, 256> invalidCharTable =
       buildInvalidQueryCharLookupTable();
-  for (const char c : value) {
+  for (const uint8_t c : value) {
     if (invalidCharTable[c]) {
       return true;
     }
diff --git a/quiche/balsa/header_properties_test.cc b/quiche/balsa/header_properties_test.cc
index f4e749a84..aee18e684 100644
--- a/quiche/balsa/header_properties_test.cc
+++ b/quiche/balsa/header_properties_test.cc
@@ -122,6 +122,11 @@ TEST(HeaderPropertiesTest, HasInvalidPathChar) {
   EXPECT_TRUE(HasInvalidPathChar("/path\rwith\tother\nwhitespace"));
   EXPECT_TRUE(HasInvalidPathChar("/backtick`"));
   EXPECT_TRUE(HasInvalidPathChar("/angle<brackets>also/bad"));
+  // Bytes >= 0x80 are not valid path characters and must be rejected
+  // without indexing the lookup table out of bounds.
+  EXPECT_TRUE(HasInvalidPathChar("/caf\xc3\xa9"));
+  EXPECT_TRUE(HasInvalidPathChar(std::string(1, '\x80')));
+  EXPECT_TRUE(HasInvalidPathChar(std::string(1, '\xff')));
 }
 
 TEST(HeaderPropertiesTest, HasInvalidQueryChar) {
@@ -143,6 +148,11 @@ TEST(HeaderPropertiesTest, HasInvalidQueryChar) {
   EXPECT_TRUE(HasInvalidQueryChar("query with spaces"));
   EXPECT_TRUE(HasInvalidQueryChar("query\rwith\tother\nwhitespace"));
   EXPECT_TRUE(HasInvalidQueryChar("query_with_angle<brackets>also_bad"));
+  // Bytes >= 0x80 are not valid query characters and must be rejected
+  // without indexing the lookup table out of bounds.
+  EXPECT_TRUE(HasInvalidQueryChar("caf\xc3\xa9"));
+  EXPECT_TRUE(HasInvalidQueryChar(std::string(1, '\x80')));
+  EXPECT_TRUE(HasInvalidQueryChar(std::string(1, '\xff')));
 }
 
 TEST(HeaderPropertiesTest, IsValidTokenVsHasInvalidHeaderChars) {