diff --git a/Tests/test_imagecms.py b/Tests/test_imagecms.py
index 55f72c3b9..dbbd46dcf 100644
--- a/Tests/test_imagecms.py
+++ b/Tests/test_imagecms.py
@@ -678,7 +678,8 @@ def test_auxiliary_channels_isolated() -> None:
 
 def test_long_modes() -> None:
     p = ImageCms.getOpenProfile("Tests/icc/sGrey-v2-nano.icc")
-    ImageCms.buildTransform(p, p, "ABCDEFGHI", "ABCDEFGHI")
+    with pytest.warns(DeprecationWarning):
+        ImageCms.buildTransform(p, p, "ABCDEFGHI", "ABCDEFGHI")
 
 
 @pytest.mark.parametrize("mode", ("RGB", "RGBA", "RGBX"))
@@ -699,3 +700,9 @@ def test_deprecation() -> None:
         assert ImageCms.VERSION == "1.0.0 pil"
     with pytest.warns(DeprecationWarning):
         assert isinstance(ImageCms.FLAGS, dict)
+
+    profile = ImageCmsProfile(ImageCms.createProfile("sRGB"))
+    with pytest.warns(DeprecationWarning):
+        ImageCms.ImageCmsTransform(profile, profile, "RGBA;16B", "RGB")
+    with pytest.warns(DeprecationWarning):
+        ImageCms.ImageCmsTransform(profile, profile, "RGB", "RGBA;16B")
diff --git a/docs/deprecations.rst b/docs/deprecations.rst
index 627672e1f..e6566eae2 100644
--- a/docs/deprecations.rst
+++ b/docs/deprecations.rst
@@ -107,6 +107,15 @@ BGR;15, BGR 16 and BGR;24
 
 The experimental BGR;15, BGR;16 and BGR;24 modes have been deprecated.
 
+Non-image modes in ImageCms
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. deprecated:: 10.4.0
+
+The use in :py:mod:`.ImageCms` of input modes and output modes that are not Pillow
+image modes has been deprecated. Defaulting to "L" or "1" if the mode cannot be mapped
+is also deprecated.
+
 Support for LibTIFF earlier than 4
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/docs/releasenotes/10.4.0.rst b/docs/releasenotes/10.4.0.rst
index 44727efd4..96300c008 100644
--- a/docs/releasenotes/10.4.0.rst
+++ b/docs/releasenotes/10.4.0.rst
@@ -28,6 +28,13 @@ BGR;15, BGR 16 and BGR;24
 
 The experimental BGR;15, BGR;16 and BGR;24 modes have been deprecated.
 
+Non-image modes in ImageCms
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The use in :py:mod:`.ImageCms` of input modes and output modes that are not Pillow
+image modes has been deprecated. Defaulting to "L" or "1" if the mode cannot be mapped
+is also deprecated.
+
 Support for LibTIFF earlier than 4
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/src/PIL/ImageCms.py b/src/PIL/ImageCms.py
index 19a79facc..ec10230f1 100644
--- a/src/PIL/ImageCms.py
+++ b/src/PIL/ImageCms.py
@@ -299,6 +299,31 @@ class ImageCmsTransform(Image.ImagePointHandler):
         proof_intent: Intent = Intent.ABSOLUTE_COLORIMETRIC,
         flags: Flags = Flags.NONE,
     ):
+        supported_modes = (
+            "RGB",
+            "RGBA",
+            "RGBX",
+            "CMYK",
+            "I;16",
+            "I;16L",
+            "I;16B",
+            "YCbCr",
+            "LAB",
+            "L",
+            "1",
+        )
+        for mode in (input_mode, output_mode):
+            if mode not in supported_modes:
+                deprecate(
+                    mode,
+                    12,
+                    {
+                        "L;16": "I;16 or I;16L",
+                        "L:16B": "I;16B",
+                        "YCCA": "YCbCr",
+                        "YCC": "YCbCr",
+                    }.get(mode),
+                )
         if proof is None:
             self.transform = core.buildTransform(
                 input.profile, output.profile, input_mode, output_mode, intent, flags
diff --git a/src/_imagingcms.c b/src/_imagingcms.c
index 2b9612db7..590e1b983 100644
--- a/src/_imagingcms.c
+++ b/src/_imagingcms.c
@@ -223,20 +223,22 @@ findLCMStype(char *PILmode) {
     if (strcmp(PILmode, "CMYK") == 0) {
         return TYPE_CMYK_8;
     }
-    if (strcmp(PILmode, "L;16") == 0) {
+    if (strcmp(PILmode, "I;16") == 0 || strcmp(PILmode, "I;16L") == 0 ||
+        strcmp(PILmode, "L;16") == 0) {
         return TYPE_GRAY_16;
     }
-    if (strcmp(PILmode, "L;16B") == 0) {
+    if (strcmp(PILmode, "I;16B") == 0 || strcmp(PILmode, "L;16B") == 0) {
         return TYPE_GRAY_16_SE;
     }
-    if (strcmp(PILmode, "YCCA") == 0 || strcmp(PILmode, "YCC") == 0) {
+    if (strcmp(PILmode, "YCbCr") == 0 || strcmp(PILmode, "YCCA") == 0 ||
+        strcmp(PILmode, "YCC") == 0) {
         return TYPE_YCbCr_8;
     }
     if (strcmp(PILmode, "LAB") == 0) {
         // LabX equivalent like ALab, but not reversed -- no #define in lcms2
         return (COLORSPACE_SH(PT_LabV2) | CHANNELS_SH(3) | BYTES_SH(1) | EXTRA_SH(1));
     }
-    /* presume "L" by default */
+    /* presume "1" or "L" by default */
     return TYPE_GRAY_8;
 }