diff --git a/src/regexp.js b/src/regexp.js
index 96ef9212e..cb4935815 100644
--- a/src/regexp.js
+++ b/src/regexp.js
@@ -289,15 +289,16 @@ pp.validateRegExp_eatAssertion = function(state) {
 
   // Lookahead / Lookbehind
   if (state.eat(LEFT_PARENTHESIS) && state.eat(QUESTION_MARK)) {
+    let lookbehind = false
     if (this.options.ecmaVersion >= 9) {
-      state.eat(LESS_THAN_SIGN)
+      lookbehind = state.eat(LESS_THAN_SIGN)
     }
     if (state.eat(EQUALS_SIGN) || state.eat(EXCLAMATION_MARK)) {
       this.validateRegExp_disjunction(state)
       if (!state.eat(RIGHT_PARENTHESIS)) {
         state.raise("Unterminated group")
       }
-      state.lastAssertionIsQuantifiable = true
+      state.lastAssertionIsQuantifiable = !lookbehind
       return true
     }
   }
diff --git a/test/tests-regexp-2018.js b/test/tests-regexp-2018.js
index 1add3a75e..0a48fabb7 100644
--- a/test/tests-regexp-2018.js
+++ b/test/tests-regexp-2018.js
@@ -118,23 +118,23 @@ testFail("/(?<!a)/u", "Invalid regular expression: /(?<!a)/: Invalid group (1:1)
 test("/(?<!a)/", {}, { ecmaVersion: 2018 })
 test("/(?<!a)/u", {}, { ecmaVersion: 2018 })
 
-test("/(?<=a)?/", {}, { ecmaVersion: 2018 })
-testFail("/(?<=a)?/u", "Invalid regular expression: /(?<=a)?/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
-test("/(?<=a)+/", {}, { ecmaVersion: 2018 })
-testFail("/(?<=a)+/u", "Invalid regular expression: /(?<=a)+/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
-test("/(?<=a)*/", {}, { ecmaVersion: 2018 })
-testFail("/(?<=a)*/u", "Invalid regular expression: /(?<=a)*/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
-test("/(?<=a){1}/", {}, { ecmaVersion: 2018 })
-testFail("/(?<=a){1}/u", "Invalid regular expression: /(?<=a){1}/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a)?/", "Invalid regular expression: /(?<=a)?/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a)?/u", "Invalid regular expression: /(?<=a)?/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a)+/", "Invalid regular expression: /(?<=a)+/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a)+/u", "Invalid regular expression: /(?<=a)+/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a)*/", "Invalid regular expression: /(?<=a)*/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a)*/u", "Invalid regular expression: /(?<=a)*/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a){1}/", "Invalid regular expression: /(?<=a){1}/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<=a){1}/u", "Invalid regular expression: /(?<=a){1}/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
 
-test("/(?<!a)?/", {}, { ecmaVersion: 2018 })
-testFail("/(?<!a)?/u", "Invalid regular expression: /(?<!a)?/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
-test("/(?<!a)+/", {}, { ecmaVersion: 2018 })
-testFail("/(?<!a)+/u", "Invalid regular expression: /(?<!a)+/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
-test("/(?<!a)*/", {}, { ecmaVersion: 2018 })
-testFail("/(?<!a)*/u", "Invalid regular expression: /(?<!a)*/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
-test("/(?<!a){1}/", {}, { ecmaVersion: 2018 })
-testFail("/(?<!a){1}/u", "Invalid regular expression: /(?<!a){1}/: Invalid quantifier (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a)?/", "Invalid regular expression: /(?<!a)?/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a)?/u", "Invalid regular expression: /(?<!a)?/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a)+/", "Invalid regular expression: /(?<!a)+/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a)+/u", "Invalid regular expression: /(?<!a)+/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a)*/", "Invalid regular expression: /(?<!a)*/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a)*/u", "Invalid regular expression: /(?<!a)*/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a){1}/", "Invalid regular expression: /(?<!a){1}/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
+testFail("/(?<!a){1}/u", "Invalid regular expression: /(?<!a){1}/: Nothing to repeat (1:1)", { ecmaVersion: 2018 })
 
 test("/(?<=(?<a>\\w){3})f/u", {}, { ecmaVersion: 2018 })
 test("/((?<=\\w{3}))f/u", {}, { ecmaVersion: 2018 })