diff --git a/dagrt/data.py b/dagrt/data.py
index 92ff198..298a10c 100644
--- a/dagrt/data.py
+++ b/dagrt/data.py
@@ -318,21 +318,42 @@ def map_variable(self, expr):
                 "nothing known about '%s'"
                 % expr.name)
 
-    def map_expr_with_children(self, children):
+    def map_sum(self, expr):
+        kind = None
+
+        last_exc = None
+
+        # Sums must be homogeneous, so being able to
+        # infer one child is good enough.
+        for ch in expr.children:
+            try:
+                ch_kind = self.rec(ch)
+            except UnableToInferKind as e:
+                if self.check:
+                    raise
+                else:
+                    last_exc = e
+
+            else:
+                kind = unify(kind, ch_kind)
+
+        if kind is None:
+            raise last_exc
+        else:
+            return kind
+
+    def map_product_like(self, children):
         kind = None
         for ch in children:
             kind = unify(kind, self.rec(ch))
 
         return kind
 
-    def map_sum(self, expr):
-        return self.map_expr_with_children(expr.children)
-
     def map_product(self, expr):
-        return self.map_expr_with_children(expr.children)
+        return self.map_product_like(expr.children)
 
     def map_quotient(self, expr):
-        return self.map_expr_with_children((expr.numerator, expr.denominator))
+        return self.map_product_like((expr.numerator, expr.denominator))
 
     def map_power(self, expr):
         if self.check and not isinstance(self.rec(expr.exponent), Scalar):
diff --git a/test/test_codegen_fortran.py b/test/test_codegen_fortran.py
index bcdb6ee..420efd3 100755
--- a/test/test_codegen_fortran.py
+++ b/test/test_codegen_fortran.py
@@ -118,7 +118,7 @@ def test_arrays_and_linalg():
 def test_self_dep_in_loop():
     with CodeBuilder(name="primary") as cb:
         cb("y", "<state>y")
-        cb("y", "5 + <func>f(0, 2*i*<func>f(0, y if i > 2 else 2*y))",
+        cb("y", "<func>f(0, 2*i*<func>f(0, y if i > 2 else 2*y))",
                 loops=(("i", 0, 5),))
         cb("<state>y", "y")