diff --git a/source/blender/blenlib/BLI_math_vector.h b/source/blender/blenlib/BLI_math_vector.h
index 42a6b90f738..5476978513e 100644
--- a/source/blender/blenlib/BLI_math_vector.h
+++ b/source/blender/blenlib/BLI_math_vector.h
@@ -108,6 +108,7 @@ MINLINE void mul_v3_v3(float r[3], const float a[3]);
 MINLINE void mul_v3_v3v3(float r[3], const float a[3], const float b[3]);
 MINLINE void mul_v4_fl(float r[4], float f);
 MINLINE void mul_v4_v4fl(float r[3], const float a[3], float f);
+MINLINE float mul_project_m4_v3_zfac(float mat[4][4], const float co[3]);
 
 MINLINE void madd_v3_v3fl(float r[3], const float a[3], float f);
 MINLINE void madd_v3_v3v3(float r[3], const float a[3], const float b[3]);
diff --git a/source/blender/blenlib/intern/math_matrix.c b/source/blender/blenlib/intern/math_matrix.c
index 69ece9b9ed0..f116c9b8443 100644
--- a/source/blender/blenlib/intern/math_matrix.c
+++ b/source/blender/blenlib/intern/math_matrix.c
@@ -367,9 +367,7 @@ void mul_mat3_m4_v3(float mat[4][4], float vec[3])
 
 void mul_project_m4_v3(float mat[4][4], float vec[3])
 {
-	const float w = (mat[0][3] * vec[0]) +
-	                (mat[1][3] * vec[1]) +
-	                (mat[2][3] * vec[2]) + mat[3][3];
+	const float w = mul_project_m4_v3_zfac(mat, vec);
 	mul_m4_v3(mat, vec);
 
 	vec[0] /= w;
diff --git a/source/blender/blenlib/intern/math_vector_inline.c b/source/blender/blenlib/intern/math_vector_inline.c
index 48e7de43a86..c8e8ff9602b 100644
--- a/source/blender/blenlib/intern/math_vector_inline.c
+++ b/source/blender/blenlib/intern/math_vector_inline.c
@@ -398,6 +398,15 @@ MINLINE void mul_v4_v4fl(float r[4], const float a[4], float f)
 	r[3] = a[3] * f;
 }
 
+/* note: could add a matrix inline */
+MINLINE float mul_project_m4_v3_zfac(float mat[4][4], const float co[3])
+{
+	return (mat[0][3] * co[0]) +
+	       (mat[1][3] * co[1]) +
+	       (mat[2][3] * co[2]) + mat[3][3];
+}
+
+
 MINLINE void madd_v2_v2fl(float r[2], const float a[2], float f)
 {
 	r[0] += a[0] * f;
diff --git a/source/blender/editors/space_view3d/view3d_project.c b/source/blender/editors/space_view3d/view3d_project.c
index 27d0010e75b..a74db71175f 100644
--- a/source/blender/editors/space_view3d/view3d_project.c
+++ b/source/blender/editors/space_view3d/view3d_project.c
@@ -276,9 +276,7 @@ eV3DProjStatus ED_view3d_project_float_object(ARegion *ar, const float co[3], fl
  */
 float ED_view3d_calc_zfac(RegionView3D *rv3d, const float co[3], bool *r_flip)
 {
-	float zfac = (rv3d->persmat[0][3] * co[0]) +
-	             (rv3d->persmat[1][3] * co[1]) +
-	             (rv3d->persmat[2][3] * co[2]) + rv3d->persmat[3][3];
+	float zfac = mul_project_m4_v3_zfac(rv3d->persmat, co);
 
 	if (r_flip) {
 		*r_flip = (zfac < 0.0f);
diff --git a/source/blender/editors/space_view3d/view3d_view.c b/source/blender/editors/space_view3d/view3d_view.c
index 5d2a351b233..d5fce1ba313 100644
--- a/source/blender/editors/space_view3d/view3d_view.c
+++ b/source/blender/editors/space_view3d/view3d_view.c
@@ -1560,11 +1560,7 @@ static void UNUSED_FUNCTION(view3d_align_axis_to_vector)(View3D *v3d, RegionView
 
 float ED_view3d_pixel_size(RegionView3D *rv3d, const float co[3])
 {
-	return (rv3d->persmat[3][3] + (
-	            rv3d->persmat[0][3] * co[0] +
-	            rv3d->persmat[1][3] * co[1] +
-	            rv3d->persmat[2][3] * co[2])
-	        ) * rv3d->pixsize * U.pixelsize;
+	return mul_project_m4_v3_zfac(rv3d->persmat, co) * rv3d->pixsize * U.pixelsize;
 }
 
 float ED_view3d_radius_to_persp_dist(const float angle, const float radius)
diff --git a/source/blender/editors/transform/transform_constraints.c b/source/blender/editors/transform/transform_constraints.c
index 35287c145c6..3088b96c339 100644
--- a/source/blender/editors/transform/transform_constraints.c
+++ b/source/blender/editors/transform/transform_constraints.c
@@ -892,9 +892,7 @@ static void setNearestAxis3d(TransInfo *t)
 	 * of two 2D points 30 pixels apart (that's the last factor in the formula) after
 	 * projecting them with ED_view3d_win_to_delta and then get the length of that vector.
 	 */
-	zfac = (t->persmat[0][3] * t->center[0]) +
-	       (t->persmat[1][3] * t->center[1]) +
-	       (t->persmat[2][3] * t->center[2]) + t->persmat[3][3];
+	zfac = mul_project_m4_v3_zfac(t->persmat, t->center);
 	zfac = len_v3(t->persinv[0]) * 2.0f / t->ar->winx * zfac * 30.0f;
 
 	for (i = 0; i < 3; i++) {