diff --git a/arraycontext/impl/pyopencl.py b/arraycontext/impl/pyopencl.py
index 575919ec6b931c35fd7d10690c817b0d711adcbc..fa2aa7493b1d4bb074c75a6b9e54a8c95acdfe11 100644
--- a/arraycontext/impl/pyopencl.py
+++ b/arraycontext/impl/pyopencl.py
@@ -346,9 +346,10 @@ class PyOpenCLArrayContext(ArrayContext):
             if "i1" in all_inames:
                 inner_iname = "i1"
         else:
-            # cannot "fit" the optimization strategy for the provided kernel
-            # => bail
-            return t_unit
+            raise RuntimeError(
+                "Unable to reason what outer_iname and inner_iname "
+                f"needs to be; all_inames is given as: {all_inames}"
+            )
 
         if inner_iname is not None:
             t_unit = lp.split_iname(t_unit, inner_iname, 16, inner_tag="l.0")