diff --git a/release/scripts/startup/bl_ui/properties_constraint.py b/release/scripts/startup/bl_ui/properties_constraint.py
index b7880e605b3..352b96c6431 100644
--- a/release/scripts/startup/bl_ui/properties_constraint.py
+++ b/release/scripts/startup/bl_ui/properties_constraint.py
@@ -420,7 +420,11 @@ class ConstraintButtonsPanel:
         row.prop(con, "use_y", text="Y")
         row.prop(con, "use_z", text="Z")
 
-        layout.prop(con, "use_offset")
+        row= layout.row()
+        row.prop(con, "use_offset")
+        row = row.row()
+        row.active = con.use_offset
+        row.prop(con, "use_add")
 
         self.space_template(layout, con)
 
diff --git a/source/blender/blenkernel/intern/constraint.c b/source/blender/blenkernel/intern/constraint.c
index ef412f0006e..f4be232b9ae 100644
--- a/source/blender/blenkernel/intern/constraint.c
+++ b/source/blender/blenkernel/intern/constraint.c
@@ -1760,7 +1760,7 @@ static void sizelike_new_data(void *cdata)
 {
 	bSizeLikeConstraint *data = (bSizeLikeConstraint *)cdata;
 
-	data->flag = SIZELIKE_X | SIZELIKE_Y | SIZELIKE_Z;
+	data->flag = SIZELIKE_X | SIZELIKE_Y | SIZELIKE_Z | SIZELIKE_MULTIPLY;
 }
 
 static void sizelike_id_looper(bConstraint *con, ConstraintIDFunc func, void *userdata)
@@ -1808,29 +1808,28 @@ static void sizelike_evaluate(bConstraint *con, bConstraintOb *cob, ListBase *ta
 		mat4_to_size(size, ct->matrix);
 		mat4_to_size(obsize, cob->matrix);
 
-		if ((data->flag & SIZELIKE_X) && (obsize[0] != 0)) {
-			if (data->flag & SIZELIKE_OFFSET) {
-				size[0] += (obsize[0] - 1.0f);
-				mul_v3_fl(cob->matrix[0], size[0] / obsize[0]);
+		if (data->flag & SIZELIKE_OFFSET) {
+			/* Scale is a multiplicative quantity, so adding it makes no sense.
+			 * However, the additive mode has to stay for backward compatibility. */
+			if (data->flag & SIZELIKE_MULTIPLY) {
+				/* size[i] *= obsize[i] */
+				mul_v3_v3(size, obsize);
 			}
-			else
-				mul_v3_fl(cob->matrix[0], size[0] / obsize[0]);
+			else {
+				/* 2.7 compatibility mode: size[i] += (obsize[i] - 1.0f) */
+				add_v3_v3(size, obsize);
+				add_v3_fl(size, -1.0f);
+			}
+		}
+
+		if ((data->flag & SIZELIKE_X) && (obsize[0] != 0)) {
+			mul_v3_fl(cob->matrix[0], size[0] / obsize[0]);
 		}
 		if ((data->flag & SIZELIKE_Y) && (obsize[1] != 0)) {
-			if (data->flag & SIZELIKE_OFFSET) {
-				size[1] += (obsize[1] - 1.0f);
-				mul_v3_fl(cob->matrix[1], size[1] / obsize[1]);
-			}
-			else
-				mul_v3_fl(cob->matrix[1], size[1] / obsize[1]);
+			mul_v3_fl(cob->matrix[1], size[1] / obsize[1]);
 		}
 		if ((data->flag & SIZELIKE_Z) && (obsize[2] != 0)) {
-			if (data->flag & SIZELIKE_OFFSET) {
-				size[2] += (obsize[2] - 1.0f);
-				mul_v3_fl(cob->matrix[2], size[2] / obsize[2]);
-			}
-			else
-				mul_v3_fl(cob->matrix[2], size[2] / obsize[2]);
+			mul_v3_fl(cob->matrix[2], size[2] / obsize[2]);
 		}
 	}
 }
diff --git a/source/blender/makesdna/DNA_constraint_types.h b/source/blender/makesdna/DNA_constraint_types.h
index e1c082748fd..e118fd39bb1 100644
--- a/source/blender/makesdna/DNA_constraint_types.h
+++ b/source/blender/makesdna/DNA_constraint_types.h
@@ -584,7 +584,8 @@ typedef enum eCopyScale_Flags {
 	SIZELIKE_X		= (1<<0),
 	SIZELIKE_Y		= (1<<1),
 	SIZELIKE_Z		= (1<<2),
-	SIZELIKE_OFFSET = (1<<3)
+	SIZELIKE_OFFSET = (1<<3),
+	SIZELIKE_MULTIPLY = (1<<4),
 } eCopyScale_Flags;
 
 /* bTransformConstraint.to/from */
diff --git a/source/blender/makesrna/intern/rna_constraint.c b/source/blender/makesrna/intern/rna_constraint.c
index 6cc9d1ef5a6..6f7580a3944 100644
--- a/source/blender/makesrna/intern/rna_constraint.c
+++ b/source/blender/makesrna/intern/rna_constraint.c
@@ -961,7 +961,12 @@ static void rna_def_constraint_size_like(BlenderRNA *brna)
 
 	prop = RNA_def_property(srna, "use_offset", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", SIZELIKE_OFFSET);
-	RNA_def_property_ui_text(prop, "Offset", "Add original scale into copied scale");
+	RNA_def_property_ui_text(prop, "Offset", "Combine original scale with copied scale");
+	RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
+
+	prop = RNA_def_property(srna, "use_add", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_negative_sdna(prop, NULL, "flag", SIZELIKE_MULTIPLY);
+	RNA_def_property_ui_text(prop, "Additive", "Use addition instead of multiplication to combine scale (2.7 compatibility)");
 	RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
 }