Index: libpng-1.2.50/scripts/libpng-config-body.in
===================================================================
--- libpng-1.2.50.orig/scripts/libpng-config-body.in
+++ libpng-1.2.50/scripts/libpng-config-body.in
@@ -7,7 +7,7 @@ Usage: libpng-config [OPTION] ...
 Known values for OPTION are:
 
   --prefix        print libpng prefix
-  --libdir        print path to directory containing library
+  --libdir        print path to directory containing library (disabled in Debian/Ubuntu)
   --libs          print library linking information
   --ccopts        print compiler options
   --cppflags      print pre-processor flags
@@ -58,6 +58,8 @@ while test $# -gt 0; do
         ;;
 
     --libdir)
+        echo >&1 "$(basename $0): --libdir option is disabled in Debian/Ubuntu"
+	exit 1
         echo ${libdir}
         ;;
 
Index: libpng-1.2.50/scripts/libpng-config.in
===================================================================
--- libpng-1.2.50.orig/scripts/libpng-config.in
+++ libpng-1.2.50/scripts/libpng-config.in
@@ -14,12 +14,13 @@
 version="@PNGLIB_VERSION@"
 prefix="@prefix@"
 exec_prefix="@exec_prefix@"
-libdir="@libdir@"
+# we disable that to make the -dev package Multi-Arch: same
+libdir=
 includedir="@includedir@/libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@"
 libs="-lpng@PNGLIB_MAJOR@@PNGLIB_MINOR@"
 all_libs="-lpng@PNGLIB_MAJOR@@PNGLIB_MINOR@ @LIBS@"
 I_opts="-I${includedir}"
-L_opts="-L${libdir}"
+L_opts=
 R_opts=""
 cppflags=""
 ccopts="@LIBPNG_NO_MMX@"
@@ -33,7 +34,7 @@ Usage: $0 [OPTION] ...
 Known values for OPTION are:
 
   --prefix        print libpng prefix
-  --libdir        print path to directory containing library
+  --libdir        print path to directory containing library (disabled in Debian/Ubuntu)
   --libs          print library linking information
   --ccopts        print compiler options
   --cppflags      print pre-processor flags
@@ -84,6 +85,8 @@ while test $# -gt 0; do
         ;;
 
     --libdir)
+        echo >&1 "$(basename $0): --libdir option is disabled in Debian/Ubuntu"
+	exit 1
         echo ${libdir}
         ;;