--- a/configure.ac
+++ b/configure.ac
@@ -61,7 +61,7 @@ fi
 AC_HEADER_STDC
 AC_CHECK_HEADERS([errno.h limits.h stddef.h stdlib.h string.h unistd.h])
 
-AM_ICONV
+m4_pattern_allow([AM_ICONV])
 # if test -n "$LIBICONV" ; then
 #   LIBS="$LIBS $LIBICONV"
 # fi
@@ -353,14 +353,14 @@ if test "$withval" != no; then
   AC_PATH_PROG([LIBPNG12_CONFIG], [libpng12-config])
   AC_PATH_PROG([LIBPNG_CONFIG], [libpng-config])
   if test -n "$LIBPNG12_CONFIG"; then
-    libpng_CPPFLAGS=`libpng12-config --cflags`
+    libpng_CPPFLAGS=`$LIBPNG12_CONFIG --cflags`
     # should be --ldopts, but it's currently broken
-    libpng_LDFLAGS=`libpng12-config --ldflags`
+    libpng_LDFLAGS=`$LIBPNG12_CONFIG --ldflags`
     libpng_LDFLAGS=`echo " $libpng_LDFLAGS" | sed 's/ -l[[^ ]][[^ ]]*//g'`
   elif test -n "$LIBPNG_CONFIG"; then
-    libpng_CPPFLAGS=`libpng-config --cflags`
+    libpng_CPPFLAGS=`$LIBPNG_CONFIG --cflags`
     # should be --ldopts, but it's currently broken
-    libpng_LDFLAGS=`libpng-config --ldflags`
+    libpng_LDFLAGS=`$LIBPNG_CONFIG --ldflags`
     libpng_LDFLAGS=`echo " $libpng_LDFLAGS" | sed 's/ -l[[^ ]][[^ ]]*//g'`
   elif test -d "$withval"; then
     libpng_CPPFLAGS="-I$withval/include"