diff --git a/src/keymap.h b/src/keymap.h
index 39837e5..16d128a 100644
--- a/src/keymap.h
+++ b/src/keymap.h
@@ -228,8 +228,13 @@
     , KE_S_XF3
     , KE_S_XF4
 
+    /* NOTE: The scroll wheel events are inverted: i.e. UP is the same as
+     * moving the actual scroll wheel down, LEFT is the same as moving the
+     * scroll wheel right. */
     , KE_MOUSEDOWN	/* scroll wheel pseudo-button Down */
     , KE_MOUSEUP	/* scroll wheel pseudo-button Up */
+    , KE_MOUSELEFT	/* scroll wheel pseudo-button Left */
+    , KE_MOUSERIGHT	/* scroll wheel pseudo-button Right */
 
     , KE_KINS		/* keypad Insert key */
     , KE_KDEL		/* keypad Delete key */
@@ -440,6 +445,8 @@
 
 #define K_MOUSEDOWN	TERMCAP2KEY(KS_EXTRA, KE_MOUSEDOWN)
 #define K_MOUSEUP	TERMCAP2KEY(KS_EXTRA, KE_MOUSEUP)
+#define K_MOUSELEFT	TERMCAP2KEY(KS_EXTRA, KE_MOUSELEFT)
+#define K_MOUSERIGHT	TERMCAP2KEY(KS_EXTRA, KE_MOUSERIGHT)
 
 #define K_CSI		TERMCAP2KEY(KS_EXTRA, KE_CSI)
 #define K_SNR		TERMCAP2KEY(KS_EXTRA, KE_SNR)