diff --git a/source/blender/blenkernel/BKE_key.h b/source/blender/blenkernel/BKE_key.h
index fe083ebe847..31b2c7dc2b9 100644
--- a/source/blender/blenkernel/BKE_key.h
+++ b/source/blender/blenkernel/BKE_key.h
@@ -109,6 +109,8 @@ void    BKE_keyblock_update_from_offset(struct Object *ob, struct KeyBlock *kb,
 /* other management */
 bool    BKE_keyblock_move(struct Object *ob, int org_index, int new_index);
 
+bool    BKE_keyblock_is_basis(struct Key *key, const int index);
+
 /* key.c */
 extern int slurph_opt;
 
diff --git a/source/blender/blenkernel/intern/key.c b/source/blender/blenkernel/intern/key.c
index d4266022d2f..b98213918bf 100644
--- a/source/blender/blenkernel/intern/key.c
+++ b/source/blender/blenkernel/intern/key.c
@@ -1890,9 +1890,23 @@ void BKE_keyblock_update_from_vertcos(Object *ob, KeyBlock *kb, float (*vertCos)
 	float *fp = kb->data;
 	int tot, a;
 
-	BLI_assert(((ob->type == OB_MESH) ? me->totvert :
-	            (ob->type == OB_LATTICE) ? lt->pntsu * lt->pntsv * lt->pntsw :
-	            ELEM(ob->type, OB_CURVE, OB_SURF) ? BKE_nurbList_verts_count(&cu->nurb) : 0) == kb->totelem);
+#ifndef NDEBUG
+	if (ob->type == OB_LATTICE) {
+		Lattice *lt = ob->data;
+		BLI_assert((lt->pntsu * lt->pntsv * lt->pntsw) == kb->totelem);
+	}
+	else if (ELEM(ob->type, OB_CURVE, OB_SURF)) {
+		Curve *cu = ob->data;
+		BLI_assert(BKE_nurbList_verts_count(&cu->nurb) == kb->totelem);
+	}
+	else if (ob->type == OB_MESH) {
+		Mesh *me = ob->data;
+		BLI_assert(me->totvert == kb->totelem);
+	}
+	else {
+		BLI_assert(0 == kb->totelem);
+	}
+#endif
 
 	tot = kb->totelem;
 	if (tot == 0) return;
@@ -2192,3 +2206,22 @@ bool BKE_keyblock_move(Object *ob, int org_index, int new_index)
 
 	return true;
 }
+
+/**
+ * Check if given keyblock (as index) is used as basis by others in given key.
+ */
+bool BKE_keyblock_is_basis(struct Key *key, const int index)
+{
+	KeyBlock *kb;
+	int i;
+
+	if (key->type == KEY_RELATIVE) {
+		for (i = 0, kb = key->block.first; kb; i++, kb = kb->next) {
+			if ((i != index) && (kb->relative == index)) {
+				return true;
+			}
+		}
+	}
+
+	return false;
+}
diff --git a/source/blender/bmesh/intern/bmesh_mesh_conv.c b/source/blender/bmesh/intern/bmesh_mesh_conv.c
index 8c96cc9addf..3630bb78b8a 100644
--- a/source/blender/bmesh/intern/bmesh_mesh_conv.c
+++ b/source/blender/bmesh/intern/bmesh_mesh_conv.c
@@ -850,15 +850,7 @@ void BM_mesh_bm_to_me(BMesh *bm, Mesh *me, bool do_tessface)
 		                                        * bmesh and the mesh are out of sync */
 		    (oldverts != NULL))                /* not used here, but 'oldverts' is used later for applying 'ofs' */
 		{
-			bool act_is_basis = false;
-
-			/* find if this key is a basis for any others */
-			for (currkey = me->key->block.first; currkey; currkey = currkey->next) {
-				if (bm->shapenr - 1 == currkey->relative) {
-					act_is_basis = true;
-					break;
-				}
-			}
+			const bool act_is_basis = BKE_keyblock_is_basis(me->key, bm->shapenr - 1);
 
 			/* active key is a base */
 			if (act_is_basis && (cd_shape_keyindex_offset != -1)) {
diff --git a/source/blender/editors/curve/editcurve.c b/source/blender/editors/curve/editcurve.c
index c279e83ad7d..d1208b8ba1c 100644
--- a/source/blender/editors/curve/editcurve.c
+++ b/source/blender/editors/curve/editcurve.c
@@ -766,16 +766,7 @@ static void calc_shapeKeys(Object *obedit)
 
 		/* editing the base key should update others */
 		if (cu->key->type == KEY_RELATIVE) {
-			int act_is_basis = 0;
-			/* find if this key is a basis for any others */
-			for (currkey = cu->key->block.first; currkey; currkey = currkey->next) {
-				if (editnurb->shapenr - 1 == currkey->relative) {
-					act_is_basis = 1;
-					break;
-				}
-			}
-
-			if (act_is_basis) { /* active key is a base */
+			if (BKE_keyblock_is_basis(cu->key, editnurb->shapenr - 1)) { /* active key is a base */
 				int totvec = 0;
 
 				/* Calculate needed memory to store offset */
diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index 0e6ccca85c3..1e4931ac792 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -2917,18 +2917,12 @@ void sculpt_vertcos_to_key(Object *ob, KeyBlock *kb, float (*vertCos)[3])
 {
 	Mesh *me = (Mesh *)ob->data;
 	float (*ofs)[3] = NULL;
-	int a, is_basis = 0;
+	int a;
+	const int kb_act_idx = ob->shapenr - 1;
 	KeyBlock *currkey;
 
 	/* for relative keys editing of base should update other keys */
-	if (me->key->type == KEY_RELATIVE)
-		for (currkey = me->key->block.first; currkey; currkey = currkey->next)
-			if (ob->shapenr - 1 == currkey->relative) {
-				is_basis = 1;
-				break;
-			}
-
-	if (is_basis) {
+	if (BKE_keyblock_is_basis(me->key, kb_act_idx)) {
 		ofs = BKE_keyblock_convert_to_vertcos(ob, kb);
 
 		/* calculate key coord offsets (from previous location) */
@@ -2937,14 +2931,10 @@ void sculpt_vertcos_to_key(Object *ob, KeyBlock *kb, float (*vertCos)[3])
 		}
 
 		/* apply offsets on other keys */
-		currkey = me->key->block.first;
-		while (currkey) {
-			int apply_offset = ((currkey != kb) && (ob->shapenr - 1 == currkey->relative));
-
-			if (apply_offset)
+		for (currkey = me->key->block.first; currkey; currkey = currkey->next) {
+			if ((currkey != kb) && (currkey->relative == kb_act_idx)) {
 				BKE_keyblock_update_from_offset(ob, currkey, ofs);
-
-			currkey = currkey->next;
+			}
 		}
 
 		MEM_freeN(ofs);