diff --git a/app/backend/autoupdatechecker.cpp b/app/backend/autoupdatechecker.cpp
index 9d4809eb..a8a1bbe7 100644
--- a/app/backend/autoupdatechecker.cpp
+++ b/app/backend/autoupdatechecker.cpp
@@ -40,7 +40,11 @@ void AutoUpdateChecker::start()
     // We'll get a callback when this is finished
     QUrl url("https://moonlight-stream.org/updates/qt.json");
     QNetworkRequest request(url);
+#if QT_VERSION >= QT_VERSION_CHECK(5, 15, 0)
     request.setAttribute(QNetworkRequest::Http2AllowedAttribute, true);
+#else
+    request.setAttribute(QNetworkRequest::HTTP2AllowedAttribute, true);
+#endif
     m_Nam.get(request);
 #endif
 }
diff --git a/app/settings/mappingfetcher.cpp b/app/settings/mappingfetcher.cpp
index bc989ac2..07d4314a 100644
--- a/app/settings/mappingfetcher.cpp
+++ b/app/settings/mappingfetcher.cpp
@@ -29,8 +29,18 @@ void MappingFetcher::start()
 
     QUrl url("https://moonlight-stream.org/SDL_GameControllerDB/gamecontrollerdb.txt");
     QNetworkRequest request(url);
-    request.setAttribute(QNetworkRequest::Http2AllowedAttribute, true);
 
+#if QT_VERSION >= QT_VERSION_CHECK(5, 15, 0)
+    request.setAttribute(QNetworkRequest::Http2AllowedAttribute, true);
+#else
+    request.setAttribute(QNetworkRequest::HTTP2AllowedAttribute, true);
+#endif
+
+    // Qt 5.12 introduced QNetworkRequest::IfModifiedSinceHeader. We _could_ implement it
+    // by hand (including QDateTime conversion to the correct string form) for earlier Qt
+    // versions, but that's a pain and this is just an optimization anyway. We'll do a bit
+    // of extra work on those legacy Qt versions by fetching the GCDB each time we launch.
+#if QT_VERSION >= QT_VERSION_CHECK(5, 12, 0)
     // Only download the file if it's newer than what we have
     QFileInfo existingFileInfo = Path::getCacheFileInfo("gamecontrollerdb.txt");
     if (existingFileInfo.exists()) {
@@ -41,6 +51,7 @@ void MappingFetcher::start()
             Path::deleteCacheFile("gamecontrollerdb.txt");
         }
     }
+#endif
 
     // We'll get a callback when this is finished
     m_Nam.get(request);