diff --git a/openapi_core/templating/media_types/finders.py b/openapi_core/templating/media_types/finders.py
index c9fa7d86..3425be96 100644
--- a/openapi_core/templating/media_types/finders.py
+++ b/openapi_core/templating/media_types/finders.py
@@ -12,8 +12,9 @@ def find(self, request):
         if request.mimetype in self.content:
             return self.content / request.mimetype, request.mimetype
 
-        for key, value in self.content.items():
-            if fnmatch.fnmatch(request.mimetype, key):
-                return value, key
+        if request.mimetype:
+            for key, value in self.content.items():
+                if fnmatch.fnmatch(request.mimetype, key):
+                    return value, key
 
         raise MediaTypeNotFound(request.mimetype, list(self.content.keys()))
diff --git a/tests/unit/templating/test_media_types_finders.py b/tests/unit/templating/test_media_types_finders.py
new file mode 100644
index 00000000..4c1fe9ef
--- /dev/null
+++ b/tests/unit/templating/test_media_types_finders.py
@@ -0,0 +1,47 @@
+import pytest
+
+from openapi_core.spec.paths import SpecPath
+from openapi_core.templating.media_types.exceptions import MediaTypeNotFound
+from openapi_core.templating.media_types.finders import MediaTypeFinder
+from openapi_core.testing import MockResponse
+
+
+class TestMediaTypes:
+    @pytest.fixture(scope="class")
+    def spec(self):
+        return {
+            "application/json": {"schema": {"type": "object"}},
+            "text/*": {"schema": {"type": "object"}},
+        }
+
+    @pytest.fixture(scope="class")
+    def content(self, spec):
+        return SpecPath.from_spec(spec)
+
+    @pytest.fixture(scope="class")
+    def finder(self, content):
+        return MediaTypeFinder(content)
+
+    def test_exact(self, finder, content):
+        response = MockResponse("", mimetype="application/json")
+
+        _, mimetype = finder.find(response)
+        assert mimetype == "application/json"
+
+    def test_match(self, finder, content):
+        response = MockResponse("", mimetype="text/html")
+
+        _, mimetype = finder.find(response)
+        assert mimetype == "text/*"
+
+    def test_not_found(self, finder, content):
+        response = MockResponse("", mimetype="unknown")
+
+        with pytest.raises(MediaTypeNotFound):
+            finder.find(response)
+
+    def test_missing(self, finder, content):
+        response = MockResponse("", mimetype=None)
+
+        with pytest.raises(MediaTypeNotFound):
+            finder.find(response)