diff --git a/spec/core/regexp/shared/new.rb b/spec/core/regexp/shared/new.rb
index 640f83f9a..44ce0a51f 100644
--- a/spec/core/regexp/shared/new.rb
+++ b/spec/core/regexp/shared/new.rb
@@ -293,9 +293,7 @@ def obj.to_int() ScratchPad.record(:called) end
     end
 
     it "raises a RegexpError if \\x is not followed by any hexadecimal digits" do
-      NATFIXME "raises a RegexpError if \\x is not followed by any hexadecimal digits", exception: SpecFailedException do
-        -> { Regexp.send(@method, "\\" + "xn") }.should raise_error(RegexpError, Regexp.new(Regexp.escape("invalid hex escape: /\\xn/")))
-      end
+      -> { Regexp.send(@method, "\\" + "xn") }.should raise_error(RegexpError, Regexp.new(Regexp.escape("invalid hex escape: /\\xn/")))
     end
 
     it "accepts an escaped string interpolation" do
diff --git a/src/regexp_object.cpp b/src/regexp_object.cpp
index 21d7a4264..e3b471466 100644
--- a/src/regexp_object.cpp
+++ b/src/regexp_object.cpp
@@ -338,9 +338,15 @@ static String prepare_pattern_for_onigmo(Env *env, const StringObject *pattern,
             }
 
             case 'x': {
+                c = next_char();
+                if (!std::isxdigit(c))
+                    env->raise("RegexpError", "invalid hex escape: /{}/", pattern->string());
+
                 *fixed_encoding = true;
                 new_pattern.append_char('\\');
                 new_pattern.append_char('x');
+                new_pattern.append_char(c);
+
                 break;
             }