diff --git a/include/crow/http_response.h b/include/crow/http_response.h
index 4ba400ba0..58562a4ae 100644
--- a/include/crow/http_response.h
+++ b/include/crow/http_response.h
@@ -242,17 +242,20 @@ namespace crow
             {
                 std::size_t last_dot = path.find_last_of(".");
                 std::string extension = path.substr(last_dot + 1);
-                std::string mimeType = "";
                 code = 200;
-                this->add_header("Content-length", std::to_string(file_info.statbuf.st_size));
+                this->add_header("Content-Length", std::to_string(file_info.statbuf.st_size));
 
-                if (extension != "")
+                if (!extension.empty())
                 {
-                    mimeType = mime_types.at(extension);
-                    if (mimeType != "")
-                        this->add_header("Content-Type", mimeType);
+                    const auto mimeType = mime_types.find(extension);
+                    if (mimeType != mime_types.end())
+                    {
+                        this->add_header("Content-Type", mimeType->second);
+                    }
                     else
-                        this->add_header("content-Type", "text/plain");
+                    {
+                        this->add_header("Content-Type", "text/plain");
+                    }
                 }
             }
             else
diff --git a/tests/img/filewith.badext b/tests/img/filewith.badext
new file mode 100644
index 000000000..afc96e20c
--- /dev/null
+++ b/tests/img/filewith.badext
@@ -0,0 +1 @@
+Test file with a strange extension.
diff --git a/tests/unittest.cpp b/tests/unittest.cpp
index 4c980993f..c4377f2f7 100644
--- a/tests/unittest.cpp
+++ b/tests/unittest.cpp
@@ -1926,8 +1926,10 @@ TEST_CASE("multipart")
 TEST_CASE("send_file")
 {
 
-    struct stat statbuf;
-    stat("tests/img/cat.jpg", &statbuf);
+    struct stat statbuf_cat;
+    stat("tests/img/cat.jpg", &statbuf_cat);
+    struct stat statbuf_badext;
+    stat("tests/img/filewith.badext", &statbuf_badext);
 
     SimpleApp app;
 
@@ -1944,6 +1946,12 @@ TEST_CASE("send_file")
         res.end();
     });
 
+    CROW_ROUTE(app, "/filewith.badext")
+    ([](const crow::request&, crow::response& res) {
+        res.set_static_file_info("tests/img/filewith.badext");
+        res.end();
+    });
+
     app.validate();
 
     //File not found check
@@ -1971,7 +1979,21 @@ TEST_CASE("send_file")
 
         CHECK(200 == res.code);
         CHECK("image/jpeg" == res.headers.find("Content-Type")->second);
-        CHECK(to_string(statbuf.st_size) == res.headers.find("Content-Length")->second);
+        CHECK(to_string(statbuf_cat.st_size) == res.headers.find("Content-Length")->second);
+    }
+
+    //Unknown extension check
+    {
+        request req;
+        response res;
+
+        req.url = "/filewith.badext";
+        req.http_ver_major = 1;
+
+        CHECK_NOTHROW(app.handle(req, res));
+        CHECK(200 == res.code);
+        CHECK("text/plain" == res.headers.find("Content-Type")->second);
+        CHECK(to_string(statbuf_badext.st_size) == res.headers.find("Content-Length")->second);
     }
 } // send_file