diff --git a/ANNOUNCE b/ANNOUNCE
index 929c285d7..392543587 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,4 +1,4 @@
-Libpng 1.6.18beta09 - July 1, 2015
+Libpng 1.6.18beta09 - July 3, 2015
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -95,9 +95,12 @@ Version 1.6.18beta08 [June 30, 2015]
     be used.
   Removed some unused WEIGHTED_FILTER macros from png.h and pngstruct.h
 
-Version 1.6.18beta09 [July 1, 2015]
+Version 1.6.18beta09 [July 3, 2015]
   Removed some useless typecasts from contrib/tools/png-fix-itxt.c
   Fixed a new signed-unsigned comparison in pngrtran.c (Max Stepin).
+  Replaced arbitrary use of 'extern' with #define PNG_LINKAGE_*.  To
+    preserve API compatibility, the new defines all default to "extern"
+    (requested by Jan Nijtmans).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index f1ae6243e..afda0ed15 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5280,9 +5280,12 @@ Version 1.6.18beta08 [June 30, 2015]
     be used.
   Removed some unused WEIGHTED_FILTER macros from png.h and pngstruct.h
 
-Version 1.6.18beta09 [July 1, 2015]
+Version 1.6.18beta09 [July 3, 2015]
   Removed some useless typecasts from contrib/tools/png-fix-itxt.c
   Fixed a new signed-unsigned comparison in pngrtran.c (Max Stepin).
+  Replaced arbitrary use of 'extern' with #define PNG_LINKAGE_*.  To
+    preserve API compatibility, the new defines all default to "extern"
+    (requested by Jan Nijtmans).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngconf.h b/pngconf.h
index 6ebc81035..bc7e07847 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -295,11 +295,11 @@
     * table entries, so we discard it here.  See the .dfn files in the
     * scripts directory.
     */
-#ifndef PNG_EXPORTA
 
-#  define PNG_EXPORTA(ordinal, type, name, args, attributes)\
-      PNG_FUNCTION(PNG_EXPORT_TYPE(type),(PNGAPI name),PNGARG(args), \
-        extern attributes)
+#ifndef PNG_EXPORTA
+#  define PNG_EXPORTA(ordinal, type, name, args, attributes) \
+      PNG_FUNCTION(PNG_EXPORT_TYPE(type), (PNGAPI name), PNGARG(args), \
+      PNG_LINKAGE_API attributes)
 #endif
 
 /* ANSI-C (C90) does not permit a macro to be invoked with an empty argument,
@@ -307,7 +307,7 @@
  */
 #define PNG_EMPTY /*empty list*/
 
-#define PNG_EXPORT(ordinal, type, name, args)\
+#define PNG_EXPORT(ordinal, type, name, args) \
    PNG_EXPORTA(ordinal, type, name, args, PNG_EMPTY)
 
 /* Use PNG_REMOVED to comment out a removed interface. */
diff --git a/pngpriv.h b/pngpriv.h
index d9bb34061..cefb6267b 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -252,17 +252,18 @@
  * always be used to declare an extern data or function object in this file.
  */
 #ifndef PNG_INTERNAL_DATA
-#  define PNG_INTERNAL_DATA(type, name, array) extern type name array
+#  define PNG_INTERNAL_DATA(type, name, array) PNG_LINKAGE_DATA type name array
 #endif
 
 #ifndef PNG_INTERNAL_FUNCTION
 #  define PNG_INTERNAL_FUNCTION(type, name, args, attributes)\
-      extern PNG_FUNCTION(type, name, args, PNG_EMPTY attributes)
+      PNG_LINKAGE_FUNCTION PNG_FUNCTION(type, name, args, PNG_EMPTY attributes)
 #endif
 
 #ifndef PNG_INTERNAL_CALLBACK
 #  define PNG_INTERNAL_CALLBACK(type, name, args, attributes)\
-      extern PNG_FUNCTION(type, (PNGCBAPI name), args, PNG_EMPTY attributes)
+      PNG_LINKAGE_CALLBACK PNG_FUNCTION(type, (PNGCBAPI name), args,\
+         PNG_EMPTY attributes)
 #endif
 
 /* If floating or fixed point APIs are disabled they may still be compiled
diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
index 47701dd95..07293ae64 100644
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -249,6 +249,17 @@ setting Z_DEFAULT_STRATEGY default @Z_FILTERED
 setting Z_DEFAULT_NOFILTER_STRATEGY default @Z_DEFAULT_STRATEGY
 setting ZLIB_VERNUM default @ZLIB_VERNUM
 
+# Linkage of:
+#
+#  API:      libpng API functions
+#  CALLBACK: internal non-file-local callbacks
+#  FUNCTION: internal non-file-local functions
+#  DATA:     internal non-file-local (const) data
+setting LINKAGE_API default extern
+setting LINKAGE_CALLBACK default extern
+setting LINKAGE_FUNCTION default extern
+setting LINKAGE_DATA default extern
+
 setting TEXT_Z_DEFAULT_COMPRESSION default @Z_DEFAULT_COMPRESSION
 setting TEXT_Z_DEFAULT_STRATEGY default @Z_DEFAULT_STRATEGY
 
diff --git a/scripts/pnglibconf.h.prebuilt b/scripts/pnglibconf.h.prebuilt
index 3f4ab251d..db60d2a1f 100644
--- a/scripts/pnglibconf.h.prebuilt
+++ b/scripts/pnglibconf.h.prebuilt
@@ -2,7 +2,7 @@
 
 /* pnglibconf.h - library build configuration */
 
-/* Libpng version 1.6.18beta09 - June 30, 2015 */
+/* Libpng version 1.6.18beta09 - July 3, 2015 */
 
 /* Copyright (c) 1998-2014 Glenn Randers-Pehrson */
 
@@ -190,6 +190,10 @@
 #define PNG_GAMMA_THRESHOLD_FIXED 5000
 #define PNG_IDAT_READ_SIZE PNG_ZBUF_SIZE
 #define PNG_INFLATE_BUF_SIZE 1024
+#define PNG_LINKAGE_API extern
+#define PNG_LINKAGE_CALLBACK extern
+#define PNG_LINKAGE_DATA extern
+#define PNG_LINKAGE_FUNCTION extern
 #define PNG_MAX_GAMMA_8 11
 #define PNG_QUANTIZE_BLUE_BITS 5
 #define PNG_QUANTIZE_GREEN_BITS 5