diff --git a/tests/routes/test_cog.py b/tests/routes/test_cog.py
index 6e8d0ea49..2f70e9847 100644
--- a/tests/routes/test_cog.py
+++ b/tests/routes/test_cog.py
@@ -240,6 +240,18 @@ def test_tile(rio, app):
     assert response.status_code == 200
     assert response.headers["content-type"] == "image/png"
 
+    cmap = urlencode({"colormap": json.dumps({"1": [58, 102]})})
+    response = app.get(
+        f"/cog/tiles/8/53/50.png?url=https://myurl.com/above_cog.tif&bidx=1&{cmap}"
+    )
+    assert response.status_code == 400
+
+    cmap = urlencode({"colormap": {"1": "#ddcb9aFF"}})
+    response = app.get(
+        f"/cog/tiles/8/53/50.png?url=https://myurl.com/above_cog.tif&bidx=1&{cmap}"
+    )
+    assert response.status_code == 400
+
     response = app.get(
         "/cog/tiles/8/53/50.png?url=https://myurl.com/above_cog.tif&bidx=1&colormap_name=above&resampling_method=somethingwrong"
     )
diff --git a/titiler/dependencies.py b/titiler/dependencies.py
index a54efff42..89526d29f 100644
--- a/titiler/dependencies.py
+++ b/titiler/dependencies.py
@@ -17,7 +17,7 @@
 from .custom import tms as custom_tms
 from .utils import get_hash
 
-from fastapi import Query
+from fastapi import HTTPException, Query
 
 from starlette.requests import Request
 
@@ -78,10 +78,15 @@ def ColorMapParams(
         return cmap.get(colormap_name.value)
 
     if colormap:
-        return json.loads(
-            colormap,
-            object_hook=lambda x: {int(k): parse_color(v) for k, v in x.items()},
-        )
+        try:
+            return json.loads(
+                colormap,
+                object_hook=lambda x: {int(k): parse_color(v) for k, v in x.items()},
+            )
+        except json.JSONDecodeError:
+            raise HTTPException(
+                status_code=400, detail="Could not parse the colormap value."
+            )
 
     return None
 
diff --git a/titiler/errors.py b/titiler/errors.py
index 9375319ac..e03e1f406 100644
--- a/titiler/errors.py
+++ b/titiler/errors.py
@@ -14,6 +14,7 @@
     EmptyMosaicError,
     InvalidAssetName,
     InvalidBandName,
+    InvalidColorFormat,
     MissingAssets,
     MissingBands,
     RioTilerError,
@@ -52,6 +53,7 @@ class BadRequestError(TilerError):
     RasterioIOError: status.HTTP_404_NOT_FOUND,
     MissingBands: status.HTTP_400_BAD_REQUEST,
     MissingAssets: status.HTTP_400_BAD_REQUEST,
+    InvalidColorFormat: status.HTTP_400_BAD_REQUEST,
     InvalidAssetName: status.HTTP_404_NOT_FOUND,
     InvalidBandName: status.HTTP_404_NOT_FOUND,
     MosaicError: status.HTTP_424_FAILED_DEPENDENCY,