diff --git a/loopy/target/c/__init__.py b/loopy/target/c/__init__.py
index 6e3602eda11d5f65e8a6af2977966e946c72a718..01d26dd822e46973ad7ebb99f18ec4519e0b4585 100644
--- a/loopy/target/c/__init__.py
+++ b/loopy/target/c/__init__.py
@@ -436,7 +436,7 @@ def c_math_mangler(target, name, arg_dtypes, modify_name=True):
                 arg_dtypes=arg_dtypes)
 
     # binary functions
-    if (name in ["fmax", "fmin"]
+    if (name in ["fmax", "fmin", "copysign"]
             and len(arg_dtypes) == 2):
 
         dtype = np.find_common_type(