diff --git a/loopy/codegen/expression.py b/loopy/codegen/expression.py
index adbd3e55afcdeaca669130e4f51cfac95afc8658..9ba97a48880294e07e77d89eae8b740056a0c1f4 100644
--- a/loopy/codegen/expression.py
+++ b/loopy/codegen/expression.py
@@ -22,10 +22,10 @@ class TypeInferenceMapper(CombineMapper):
             if result.isbuiltin and other.isbuiltin:
                 result = (np.empty(0, dtype=result) + np.empty(0, dtype=other)).dtype
             elif result.isbuiltin and not other.isbuiltin:
-                # assume the non-natiev type takes over
+                # assume the non-native type takes over
                 result = other
             elif not result.isbuiltin and other.isbuiltin:
-                # assume the non-natiev type takes over
+                # assume the non-native type takes over
                 pass
             else:
                 if not result is other:
@@ -40,6 +40,15 @@ class TypeInferenceMapper(CombineMapper):
     def map_subscript(self, expr):
         return self.rec(expr.aggregate)
 
+    def map_call(self, expr):
+        from pymbolic.primitives import Variable
+        if isinstance(expr.function, Variable):
+            name = expr.function.name
+            arg_dtypes = tuple(self.rec(par) for par in expr.parameters)
+            return self.kernel.get_function_result_dtype(name, arg_dtypes)
+        else:
+            return CombineMapper.map_call(self, expr)
+
     def map_variable(self, expr):
         try:
             return self.kernel.arg_dict[expr.name].dtype
diff --git a/loopy/kernel.py b/loopy/kernel.py
index bef788c0ded57803e6db4bd25380f8534ed80269..2cb427bd3e794f0bcfb070985ac9e24444400f61 100644
--- a/loopy/kernel.py
+++ b/loopy/kernel.py
@@ -477,6 +477,14 @@ def parse_reduction_op(name):
 
 # {{{ loop kernel object
 
+def _default_get_function_result_dtype(name, arg_dtypes):
+    if len(arg_dtypes) == 1:
+        dtype, = arg_dtypes
+        return dtype
+    else:
+        raise RuntimeError("no type inference information on "
+                "function '%s'" % name)
+
 class LoopKernel(Record):
     """
     :ivar device: :class:`pyopencl.Device`
@@ -504,6 +512,7 @@ class LoopKernel(Record):
     :ivar applied_substitutions: A list of past substitution dictionaries that
         were applied to the kernel. These are stored so that they may be repeated
         on expressions the user specifies later.
+    :ivar get_function_result_dtype:
 
     :ivar cache_manager:
 
@@ -521,7 +530,8 @@ class LoopKernel(Record):
             local_sizes={},
             iname_to_tag={}, iname_to_tag_requests=None, substitutions={},
             cache_manager=None, lowest_priority_inames=[], breakable_inames=set(),
-            applied_substitutions=[]):
+            applied_substitutions=[],
+            get_function_result_dtype=_default_get_function_result_dtype):
         """
         :arg domain: a :class:`islpy.BasicSet`, or a string parseable to a basic set by the isl.
             Example: "{[i,j]: 0<=i < 10 and 0<= j < 9}"
@@ -718,7 +728,8 @@ class LoopKernel(Record):
                 cache_manager=cache_manager,
                 lowest_priority_inames=lowest_priority_inames,
                 breakable_inames=breakable_inames,
-                applied_substitutions=applied_substitutions)
+                applied_substitutions=applied_substitutions,
+                get_function_result_dtype=get_function_result_dtype)
 
     def make_unique_instruction_id(self, insns=None, based_on="insn", extra_used_ids=set()):
         if insns is None: