diff --git a/src/core/parse.c b/src/core/parse.c
index 3734d502..4ea736a0 100644
--- a/src/core/parse.c
+++ b/src/core/parse.c
@@ -273,6 +273,10 @@ static int escapeu(JanetParser *p, JanetParseState *state, uint8_t c) {
     state->argn = (state->argn << 4) + digit;
     state->counter--;
     if (!state->counter) {
+        if (state->argn > 0x10FFFF) {
+            p->error = "invalid unicode codepoint";
+            return 1;
+        }
         write_codepoint(p, state->argn);
         state->argn = 0;
         state->consumer = stringchar;
@@ -291,7 +295,7 @@ static int escape1(JanetParser *p, JanetParseState *state, uint8_t c) {
         state->argn = 0;
         state->consumer = escapeh;
     } else if (c == 'u' || c == 'U') {
-        state->counter = c == 'u' ? 4 : 8;
+        state->counter = c == 'u' ? 4 : 6;
         state->argn = 0;
         state->consumer = escapeu;
     } else {
diff --git a/test/suite0.janet b/test/suite0.janet
index f1d4432c..c42de3b0 100644
--- a/test/suite0.janet
+++ b/test/suite0.janet
@@ -206,9 +206,9 @@
 (def 🐮 :cow)
 (assert (= (string "🐼" 🦊 🐮) "🐼foxcow") "emojis 🙉 :)")
 (assert (not= 🦊 "🦊") "utf8 strings are not symbols and vice versa")
-(assert (= "\U0001F637" "😷") "unicode escape 1")
-(assert (= "\u2623" "\U00002623" "☣") "unicode escape 2")
-(assert (= "\u24c2" "\U000024c2" "Ⓜ") "unicode escape 3")
+(assert (= "\U01F637" "😷") "unicode escape 1")
+(assert (= "\u2623" "\U002623" "☣") "unicode escape 2")
+(assert (= "\u24c2" "\U0024c2" "Ⓜ") "unicode escape 3")
 (assert (= "\u0061" "a") "unicode escape 4")
 
 # Symbols with @ character
diff --git a/tools/tm_lang_gen.janet b/tools/tm_lang_gen.janet
index f19a23b8..32fcf729 100644
--- a/tools/tm_lang_gen.janet
+++ b/tools/tm_lang_gen.janet
@@ -308,7 +308,7 @@
       <array>
         <dict>
           <key>match</key>
-          <string>(\\[nevr0zft"\\']|\\x[0-9a-fA-F]{2}|\\u[0-9a-fA-F]{4}|\\U[0-9a-fA-F]{8})</string>
+          <string>(\\[nevr0zft"\\']|\\x[0-9a-fA-F]{2}|\\u[0-9a-fA-F]{4}|\\U[0-9a-fA-F]{6})</string>
           <key>name</key>
           <string>constant.character.escape.janet</string>
         </dict>