diff --git a/CHANGES b/CHANGES
index ef600db8b..0ed2cb5b9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -21,6 +21,7 @@ Other fixes:
  - GB Video: Fix some cases where SGB border doesn't draw to mutli-buffers
  - GBA: Reject incorrectly sized BIOSes
  - Qt: Fix OpenGL 2.1 support (fixes mgba.io/i/1678)
+ - Qt: Fix unmapping zipped ROM (fixes mgba.io/i/1777)
 Misc:
  - 3DS: Clean up legacy initialization (fixes mgba.io/i/1768)
  - GBA Serialize: Only flunk BIOS check if official BIOS was expected
diff --git a/src/platform/qt/CoreManager.cpp b/src/platform/qt/CoreManager.cpp
index 6b2580d3c..6b2a64f09 100644
--- a/src/platform/qt/CoreManager.cpp
+++ b/src/platform/qt/CoreManager.cpp
@@ -65,7 +65,7 @@ CoreController* CoreManager::loadGame(const QString& path) {
 		if (vfOriginal && (size = vfOriginal->size(vfOriginal)) > 0) {
 			void* mem = vfOriginal->map(vfOriginal, size, MAP_READ);
 			vf = VFileMemChunk(mem, size);
-			vfOriginal->unmap(vfOriginal, mem, (size_t) read);
+			vfOriginal->unmap(vfOriginal, mem, size);
 			vfOriginal->close(vfOriginal);
 		}
 	}