diff --git a/libmproxy/models/http.py b/libmproxy/models/http.py
index 8a0b226d4..60fcb92ce 100644
--- a/libmproxy/models/http.py
+++ b/libmproxy/models/http.py
@@ -91,10 +91,12 @@ class MessageMixin(stateobject.StateObject):
 
             Returns the number of replacements made.
         """
-        with decoded(self):
-            self.content, count = utils.safe_subn(
-                pattern, repl, self.content, *args, **kwargs
-            )
+        count = 0
+        if self.content:
+            with decoded(self):
+                self.content, count = utils.safe_subn(
+                    pattern, repl, self.content, *args, **kwargs
+                )
         fields = []
         for name, value in self.headers.fields:
             name, c = utils.safe_subn(pattern, repl, name, *args, **kwargs)
diff --git a/test/test_flow.py b/test/test_flow.py
index b8d1fad31..68316f2a4 100644
--- a/test/test_flow.py
+++ b/test/test_flow.py
@@ -463,6 +463,11 @@ class TestFlow(object):
         f.response.content = "\xc2foo"
         f.replace("foo", u"bar")
 
+    def test_replace_no_content(self):
+        f = tutils.tflow()
+        f.request.content = CONTENT_MISSING
+        assert f.replace("foo", "bar") == 0
+
     def test_replace(self):
         f = tutils.tflow(resp=True)
         f.request.headers["foo"] = "foo"