diff --git a/Tests/test_box_blur.py b/Tests/test_box_blur.py
index 8c52054a2..6224c435d 100644
--- a/Tests/test_box_blur.py
+++ b/Tests/test_box_blur.py
@@ -64,10 +64,12 @@ class TestBoxBlur(PillowTestCase):
         self.assertRaises(ValueError, self.box_blur, sample.convert("P"))
         self.box_blur(sample.convert("L"))
         self.box_blur(sample.convert("LA"))
+        self.box_blur(sample.convert("LA").convert("La"))
         self.assertRaises(ValueError, self.box_blur, sample.convert("I"))
         self.assertRaises(ValueError, self.box_blur, sample.convert("F"))
         self.box_blur(sample.convert("RGB"))
         self.box_blur(sample.convert("RGBA"))
+        self.box_blur(sample.convert("RGBA").convert("RGBa"))
         self.box_blur(sample.convert("CMYK"))
         self.assertRaises(ValueError, self.box_blur, sample.convert("YCbCr"))
 
diff --git a/libImaging/BoxBlur.c b/libImaging/BoxBlur.c
index 0fe3b7c35..854a53386 100644
--- a/libImaging/BoxBlur.c
+++ b/libImaging/BoxBlur.c
@@ -257,10 +257,12 @@ ImagingBoxBlur(Imaging imOut, Imaging imIn, float radius, int n)
 
     if (!(strcmp(imIn->mode, "RGB") == 0 ||
           strcmp(imIn->mode, "RGBA") == 0 ||
+          strcmp(imIn->mode, "RGBa") == 0 ||
           strcmp(imIn->mode, "RGBX") == 0 ||
           strcmp(imIn->mode, "CMYK") == 0 ||
           strcmp(imIn->mode, "L") == 0 ||
-          strcmp(imIn->mode, "LA") == 0))
+          strcmp(imIn->mode, "LA") == 0 ||
+          strcmp(imIn->mode, "La") == 0))
         return ImagingError_ModeError();
 
     imTransposed = ImagingNew(imIn->mode, imIn->ysize, imIn->xsize);