diff --git a/src/posix/sdl/i_input.cpp b/src/posix/sdl/i_input.cpp
index 61a1fe0be..0d45ed722 100644
--- a/src/posix/sdl/i_input.cpp
+++ b/src/posix/sdl/i_input.cpp
@@ -378,7 +378,12 @@ void MessagePump (const SDL_Event &sev)
 		else
 		{
 			event.type = EV_KeyDown;
-			event.data1 = sev.wheel.y > 0 ? KEY_MWHEELUP : KEY_MWHEELDOWN;
+
+			if (sev.wheel.y != 0)
+				event.data1 = sev.wheel.y > 0 ? KEY_MWHEELUP : KEY_MWHEELDOWN;
+			else
+				event.data1 = sev.wheel.x > 0 ? KEY_MWHEELRIGHT : KEY_MWHEELLEFT;
+
 			D_PostEvent (&event);
 			event.type = EV_KeyUp;
 			D_PostEvent (&event);