diff --git a/src/utils.jl b/src/utils.jl
index fca04ac2..5e2c5743 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -657,7 +657,7 @@ function valid_escaped_seq(s::AbstractString)
     if popfirst!(a) == '\\'
         c = popfirst!(a)
         if c === 'x' || c === 'u' || c === 'U'
-            maxiter = c === 'x' ? 2 : c === 'u' ? 4 : 5
+            maxiter = c === 'x' ? 2 : c === 'u' ? 4 : 8
             0 < length(a) <= maxiter || return false
             n = 0
             while !isempty(a)
diff --git a/test/parser.jl b/test/parser.jl
index 3c3ed204..4440ed8e 100644
--- a/test/parser.jl
+++ b/test/parser.jl
@@ -994,6 +994,7 @@ end""" |> test_expr
         @test test_expr(raw"'\u2222'")
         @test test_expr(raw"'\U2222'")
         @test test_expr(raw"'\U22222'")
+        @test test_expr(raw"'\U00000001'")
 
         @test CSTParser.parse(raw"'\200'").head == :errortoken
         @test CSTParser.parse(raw"'\300'").head == :errortoken
@@ -1009,6 +1010,7 @@ end""" |> test_expr
         @test CSTParser.parse(raw"'\u222ää'").head == :errortoken
         @test CSTParser.parse(raw"'\x222ää'").head == :errortoken
         @test CSTParser.parse(raw"'\U222ää'").head == :errortoken
+        @test CSTParser.parse(raw"'\U10000001'").head == :errortoken
         for c in rand(Char, 1000)
             @test test_expr(string("'", c, "'"))
         end