diff --git a/src/main.aap b/src/main.aap
index bedbbb5..19bc97d 100644
--- a/src/main.aap
+++ b/src/main.aap
@@ -22,11 +22,11 @@
     # A U T O C O N F
     #
 
-    # Run autoconf when configure.in has been changed since it was last run.
+    # Run autoconf when configure.ac has been changed since it was last run.
     # This is skipped when the signatures in "mysign" are up-to-date.  When
     # there is no autoconf program skip this (the signature is often the only
     # thing that's outdated)
-    auto/configure {signfile = mysign} : configure.in
+    auto/configure {signfile = mysign} : configure.ac
         @if not program_path("autoconf"):
             :print Can't find autoconf, using existing configure script.
         @else: