diff --git a/src/parser/utf8_validate.cpp b/src/parser/utf8_validate.cpp
index 50aa06d8..a4b74796 100644
--- a/src/parser/utf8_validate.cpp
+++ b/src/parser/utf8_validate.cpp
@@ -72,7 +72,7 @@ bool isValidUtf8(const char *expression, const size_t len) {
     while (i < len) {
         DEBUG_PRINTF("byte %zu: 0x%02x\n", i, s[i]);
         // One octet.
-        if (s[i] < 0x7f) {
+        if (s[i] <= 0x7f) {
             DEBUG_PRINTF("one octet\n");
             i++;
             continue;
diff --git a/unit/internal/utf8_validate.cpp b/unit/internal/utf8_validate.cpp
index 03357942..f69ee857 100644
--- a/unit/internal/utf8_validate.cpp
+++ b/unit/internal/utf8_validate.cpp
@@ -64,8 +64,8 @@ static ValidUtf8TestInfo valid_utf8_tests[] = {
     {"공동경비구역", true},
     {"জলসাঘর", true},
 
-    // Invalid one-byte caseS.
-    {"\x7f", false},
+    // Valid one-byte caseS.
+    {"\x7f", true}, // \x7f is valid
 
     // These bytes should never appear in a UTF-8 stream.
     {"\xc0", false},