1 files changed, 1 insertions, 1 deletions
diff --git a/series.mac b/series.mac
index 9dd233c..57eb528 100644
--- a/series.mac
+++ b/series.mac
@@ -137,7 +137,7 @@ mul_series(factors, max_order) := block(
   nfactors : length(factors),
 
   /* If there is nothing to multiple, still filter higher terms */
-  if is(nfactors=1) then (
+  if nfactors = 1 then (
     return(__simple_filter(factors[1], max_order))),
 
   /* Allocate stack and table for ranges */