--- configure.in        2006-10-12 16:13:01.000000000 -0300
+++ configure.in.new    2006-10-12 16:13:19.000000000 -0300
@@ -64,7 +64,7 @@
 AC_CHECK_LIB(z, gzopen,
   , AC_MSG_ERROR([*** Cannot compile without zlib.]))
 AC_CHECK_LIB(png, png_create_write_struct,
-  , AC_MSG_ERROR([*** Cannot compile without libpng.]), [-lz])
+  , AC_MSG_ERROR([*** Cannot compile without libpng.]), [-lz -lm])
 AC_CHECK_LIB(pthread, pthread_yield)
 
 dnl Checks for header files.