diff --git a/src/keymap.h b/src/keymap.h
index 613f955..ac688e2 100644
--- a/src/keymap.h
+++ b/src/keymap.h
@@ -461,6 +461,9 @@ XkbWrapGroupIntoRange(int32_t group,
                       enum xkb_range_exceed_type out_of_range_group_action,
                       xkb_layout_index_t out_of_range_group_number);
 
+xkb_mod_mask_t
+mod_mask_get_effective(struct xkb_keymap *keymap, xkb_mod_mask_t mods);
+
 struct xkb_keymap_format_ops {
     bool (*keymap_new_from_names)(struct xkb_keymap *keymap,
                                   const struct xkb_rule_names *names);
diff --git a/src/state.c b/src/state.c
index 03463c8..279a646 100644
--- a/src/state.c
+++ b/src/state.c
@@ -1071,6 +1071,28 @@ xkb_state_serialize_layout(struct xkb_state *state,
     return ret;
 }
 
+/**
+ * Gets a modifier mask and returns the resolved effective mask; this
+ * is needed because some modifiers can also map to other modifiers, e.g.
+ * the "NumLock" modifier usually also sets the "Mod2" modifier.
+ */
+xkb_mod_mask_t
+mod_mask_get_effective(struct xkb_keymap *keymap, xkb_mod_mask_t mods)
+{
+    const struct xkb_mod *mod;
+    xkb_mod_index_t i;
+    xkb_mod_mask_t mask;
+
+    /* The effective mask is only real mods for now. */
+    mask = mods & MOD_REAL_MASK_ALL;
+
+    xkb_mods_enumerate(i, mod, &keymap->mods)
+        if (mods & (1u << i))
+            mask |= mod->mapping;
+
+    return mask;
+}
+
 /**
  * Returns 1 if the given modifier is active with the specified type(s), 0 if
  * not, or -1 if the modifier is invalid.
diff --git a/src/xkbcomp/keymap.c b/src/xkbcomp/keymap.c
index cc5bc83..ec93ee4 100644
--- a/src/xkbcomp/keymap.c
+++ b/src/xkbcomp/keymap.c
@@ -32,15 +32,7 @@
 static void
 ComputeEffectiveMask(struct xkb_keymap *keymap, struct xkb_mods *mods)
 {
-    const struct xkb_mod *mod;
-    xkb_mod_index_t i;
-
-    /* The effective mask is only real mods for now. */
-    mods->mask = mods->mods & MOD_REAL_MASK_ALL;
-
-    xkb_mods_enumerate(i, mod, &keymap->mods)
-        if (mods->mods & (1u << i))
-            mods->mask |= mod->mapping;
+    mods->mask = mod_mask_get_effective(keymap, mods->mods);
 }
 
 static void