diff --git a/legacy/ethumb/configure.ac b/legacy/ethumb/configure.ac
index 9d6b907982..060b6aab2a 100644
--- a/legacy/ethumb/configure.ac
+++ b/legacy/ethumb/configure.ac
@@ -61,7 +61,7 @@ dnl we just have set the version info, then:
 AC_SUBST(version_info)
 
 AC_PROG_CC
-AM_PROG_CC_STDC
+AC_PROG_CC_STDC
 AM_PROG_CC_C_O
 AC_HEADER_STDC
 AC_C___ATTRIBUTE__