diff --git a/ANNOUNCE b/ANNOUNCE
index f33cdb1..9a3192e 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.5.5beta05 - July 29, 2011
+Libpng 1.5.5beta05 - August 17, 2011
 
 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.
@@ -45,7 +45,21 @@
   Updated commentary about the png_rgb_to_gray() default coefficients
     in the manual and in pngrtran.c
 
-Version 1.5.5beta05 [July 29, 2011]
+Version 1.5.5beta05 [August 17, 2011]
+  Prevent unexpected API exports from non-libpng DLLs on Windows.  The "_DLL"
+    is removed from the test of whether a DLL is being built (this erroneously
+    caused the libpng APIs to be marked as DLL exports in static builds under
+    Microsoft Visual Studio).  Almost all of the libpng building configuration
+    is moved from pngconf.h to pngpriv.h, but PNG_DLL_EXPORT remains in
+    pngconf.h, though, so that it is colocated with the import definition (it
+    is no longer used anywhere in the installed headers).  The VStudio project
+    definitions have been cleaned up: "_USRDLL" has been removed from the
+    static library builds (this was incorrect), and PNG_USE_DLL has been added
+    to pngvalid to test the functionality (pngtest does not supply it,
+    deliberately).  The spurious "_EXPORTS" has been removed from the
+    libpng build (all these errors were a result of copy/paste between project
+    configurations.)
+
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index a55a850..a463383 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3529,7 +3529,20 @@
   Updated commentary about the png_rgb_to_gray() default coefficients
     in the manual and in pngrtran.c
 
-Version 1.5.5beta05 [July 29, 2011]
+Version 1.5.5beta05 [August 17, 2011]
+  Prevent unexpected API exports from non-libpng DLLs on Windows.  The "_DLL"
+    is removed from the test of whether a DLL is being built (this erroneously
+    caused the libpng APIs to be marked as DLL exports in static builds under
+    Microsoft Visual Studio).  Almost all of the libpng building configuration
+    is moved from pngconf.h to pngpriv.h, but PNG_DLL_EXPORT remains in
+    pngconf.h, though, so that it is colocated with the import definition (it
+    is no longer used anywhere in the installed headers).  The VStudio project
+    definitions have been cleaned up: "_USRDLL" has been removed from the
+    static library builds (this was incorrect), and PNG_USE_DLL has been added
+    to pngvalid to test the functionality (pngtest does not supply it,
+    deliberately).  The spurious "_EXPORTS" has been removed from the
+    libpng build (all these errors were a result of copy/paste between project
+    configurations.)
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngconf.h b/pngconf.h
index c087df3..cd183e3 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.5.5beta05 - July 29, 2011
+ * libpng version 1.5.5beta05 - August 17, 2011
  *
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -164,7 +164,9 @@
  *                       'type', compiler specific.
  *
  * PNG_DLL_EXPORT Set to the magic to use during a libpng build to
- *                make a symbol exported from the DLL.
+ *                make a symbol exported from the DLL.  Not used in the
+ *                public header files; see pngpriv.h for how it is used
+ *                in the libpng build.
  *
  * PNG_DLL_IMPORT Set to the magic to force the libpng symbols to come
  *                from a DLL - used to define PNG_IMPEXP when
@@ -258,25 +260,14 @@
 #  define PNGAPI PNGCAPI
 #endif
 
-/* The default for PNG_IMPEXP depends on whether the library is
- * being built or used.
+/* PNG_IMPEXP may be set on the compilation system command line or (if not set)
+ * then in an internal header file when building the library, otherwise (when
+ * using the library) it is set here.
  */
 #ifndef PNG_IMPEXP
-#  ifdef PNGLIB_BUILD
-    /* Building the library */
-#    if (defined(DLL_EXPORT)/*from libtool*/ ||\
-        defined(_WINDLL) || defined(_DLL) || defined(__DLL__) ||\
-        defined(_USRDLL) ||\
-        defined(PNG_BUILD_DLL)) && defined(PNG_DLL_EXPORT)
-      /* Building a DLL. */
-#      define PNG_IMPEXP PNG_DLL_EXPORT
-#    endif /* DLL */
-#  else
-    /* Using the library */
-#    if defined(PNG_USE_DLL) && defined(PNG_DLL_IMPORT)
-      /* This forces use of a DLL, disallowing static linking */
-#      define PNG_IMPEXP PNG_DLL_IMPORT
-#    endif
+#  if defined(PNG_USE_DLL) && defined(PNG_DLL_IMPORT)
+     /* This forces use of a DLL, disallowing static linking */
+#    define PNG_IMPEXP PNG_DLL_IMPORT
 #  endif
 
 #  ifndef PNG_IMPEXP
@@ -356,25 +347,18 @@
 #    ifndef PNG_ALLOCATED
 #      define PNG_ALLOCATED  __attribute__((__malloc__))
 #    endif
-
-    /* This specifically protects structure members that should only be
-     * accessed from within the library, therefore should be empty during
-     * a library build.
-     */
-#    ifndef PNGLIB_BUILD
-#      ifndef PNG_DEPRECATED
-#        define PNG_DEPRECATED __attribute__((__deprecated__))
+#    ifndef PNG_DEPRECATED
+#      define PNG_DEPRECATED __attribute__((__deprecated__))
+#    endif
+#    ifndef PNG_PRIVATE
+#      if 0 /* Doesn't work so we use deprecated instead*/
+#        define PNG_PRIVATE \
+          __attribute__((warning("This function is not exported by libpng.")))
+#      else
+#        define PNG_PRIVATE \
+          __attribute__((__deprecated__))
 #      endif
-#      ifndef PNG_PRIVATE
-#        if 0 /* Doesn't work so we use deprecated instead*/
-#          define PNG_PRIVATE \
-            __attribute__((warning("This function is not exported by libpng.")))
-#        else
-#          define PNG_PRIVATE \
-            __attribute__((__deprecated__))
-#        endif
-#      endif
-#    endif /* PNGLIB_BUILD */
+#    endif
 #  endif /* __GNUC__ */
 
 #  if defined(_MSC_VER)  && (_MSC_VER >= 1300)
@@ -389,19 +373,12 @@
 #        define PNG_ALLOCATED __declspec(restrict)
 #      endif
 #    endif
-
-    /* This specifically protects structure members that should only be
-     * accessed from within the library, therefore should be empty during
-     * a library build.
-     */
-#    ifndef PNGLIB_BUILD
-#      ifndef PNG_DEPRECATED
-#        define PNG_DEPRECATED __declspec(deprecated)
-#      endif
-#      ifndef PNG_PRIVATE
-#        define PNG_PRIVATE __declspec(deprecated)
-#      endif
-#    endif /* PNGLIB_BUILD */
+#    ifndef PNG_DEPRECATED
+#      define PNG_DEPRECATED __declspec(deprecated)
+#    endif
+#    ifndef PNG_PRIVATE
+#      define PNG_PRIVATE __declspec(deprecated)
+#    endif
 #  endif /* _MSC_VER */
 #endif /* PNG_PEDANTIC_WARNINGS */
 
diff --git a/pngpriv.h b/pngpriv.h
index 5b4d212..f38d603 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -44,7 +44,8 @@
  */
 #include <stdlib.h>
 
-#define PNGLIB_BUILD
+#define PNGLIB_BUILD /*libpng is being built, not used*/
+
 #ifdef PNG_USER_CONFIG
 #  include "pngusr.h"
    /* These should have been defined in pngusr.h */
@@ -55,10 +56,80 @@
 #    define PNG_USER_DLLFNAME_POSTFIX "Cb"
 #  endif
 #endif
+
+/* Is this a build of a DLL where compilation of the object modules requires
+ * different preprocessor settings to those required for a simple library?  If
+ * so PNG_BUILD_DLL must be set.
+ *
+ * If libpng is used inside a DLL but that DLL does not export the libpng APIs
+ * PNG_BUILD_DLL must not be set.  To avoid the code below kicking in build a
+ * static library of libpng then link the DLL against that.
+ */
+#ifndef PNG_BUILD_DLL
+#  ifdef DLL_EXPORT
+      /* This is set by libtool when files are compiled for a DLL; libtool
+       * always compiles twice, even on systems where it isn't necessary.  Set
+       * PNG_BUILD_DLL in case it is necessary:
+       */
+#     define PNG_BUILD_DLL
+#  else
+#     ifdef _WINDLL
+         /* This is set by the Microsoft Visual Studio IDE in projects that
+          * build a DLL.  It can't easily be removed from those projects (it
+          * isn't visible in the Visual Studio UI) so it is a fairly reliable
+          * indication that PNG_IMPEXP needs to be set to the DLL export
+          * attributes.
+          */
+#        define PNG_BUILD_DLL
+#     else
+#        ifdef __DLL__
+            /* This is set by the Borland C system when compiling for a DLL
+             * (as above.)
+             */
+#           define PNG_BUILD_DLL
+#        else
+            /* Add additional compiler cases here. */
+#        endif
+#     endif
+#  endif
+#endif /* Setting PNG_BUILD_DLL if required */
+
+/* See pngconf.h for more details: the builder of the library may set this on
+ * the command line to the right thing for the specific compilation system or it
+ * may be automagically set above (at present we know of no system where it does
+ * need to be set on the command line.)
+ *
+ * PNG_IMPEXP must be set here when building the library to prevent pngconf.h
+ * setting it to the "import" setting for a DLL build.
+ */
+#ifndef PNG_IMPEXP
+#  ifdef PNG_BUILD_DLL
+#     define PNG_IMPEXP PNG_DLL_EXPORT
+#  else
+      /* Not building a DLL, or the DLL doesn't require specific export
+       * definitions.
+       */
+#     define PNG_IMPEXP
+#  endif
+#endif
+
+/* No warnings for private or deprecated functions in the build: */
+#ifndef PNG_DEPRECATED
+#  define PNG_DEPRECATED
+#endif
+#ifndef PNG_PRIVATE
+#  define PNG_PRIVATE
+#endif
+
 #include "png.h"
 #include "pnginfo.h"
 #include "pngstruct.h"
 
+/* pngconf.h does not set PNG_DLL_EXPORT unless it is required, so: */
+#ifndef PNG_DLL_EXPORT
+#  define PNG_DLL_EXPORT
+#endif
+
 /* This is used for 16 bit gamma tables - only the top level pointers are const,
  * this could be changed:
  */
@@ -1078,6 +1149,7 @@
     unsigned long *hi_product, unsigned long *lo_product));
 #endif
 
+#ifdef PNG_cHRM_SUPPORTED
 /* Added at libpng version 1.4.0 */
 PNG_EXTERN void png_check_IHDR PNGARG((png_structp png_ptr,
     png_uint_32 width, png_uint_32 height, int bit_depth,
diff --git a/projects/vstudio/libpng/libpng.vcxproj b/projects/vstudio/libpng/libpng.vcxproj
index 6977900..c4bf041 100644
--- a/projects/vstudio/libpng/libpng.vcxproj
+++ b/projects/vstudio/libpng/libpng.vcxproj
@@ -118,7 +118,7 @@
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
       <Optimization>Disabled</Optimization>
       <BasicRuntimeChecks>EnableFastChecks</BasicRuntimeChecks>
-      <PreprocessorDefinitions>WIN32;_DEBUG;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_WINDOWS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <IntrinsicFunctions>true</IntrinsicFunctions>
       <FunctionLevelLinking>true</FunctionLevelLinking>
       <FloatingPointExceptions>false</FloatingPointExceptions>
@@ -175,7 +175,7 @@
       <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
       <FunctionLevelLinking>true</FunctionLevelLinking>
       <IntrinsicFunctions>true</IntrinsicFunctions>
-      <PreprocessorDefinitions>WIN32;NDEBUG;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_WINDOWS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <FloatingPointExceptions>false</FloatingPointExceptions>
       <TreatWChar_tAsBuiltInType>false</TreatWChar_tAsBuiltInType>
       <PrecompiledHeaderFile>pngpriv.h</PrecompiledHeaderFile>
diff --git a/projects/vstudio/pngvalid/pngvalid.vcxproj b/projects/vstudio/pngvalid/pngvalid.vcxproj
index 79fd1bd..bd85806 100644
--- a/projects/vstudio/pngvalid/pngvalid.vcxproj
+++ b/projects/vstudio/pngvalid/pngvalid.vcxproj
@@ -81,7 +81,7 @@
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
       <Optimization>Disabled</Optimization>
       <BasicRuntimeChecks>EnableFastChecks</BasicRuntimeChecks>
-      <PreprocessorDefinitions>WIN32;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_CONSOLE;PNG_USE_DLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(ZLibSrcDir);..\..\..\scripts;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <DisableSpecificWarnings>4996;4127</DisableSpecificWarnings>
       <CompileAsManaged>false</CompileAsManaged>
@@ -146,7 +146,7 @@
       <Optimization>Full</Optimization>
       <FunctionLevelLinking>false</FunctionLevelLinking>
       <IntrinsicFunctions>true</IntrinsicFunctions>
-      <PreprocessorDefinitions>WIN32;NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_CONSOLE;PNG_USE_DLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$(ZLibSrcDir);..\..\..\scripts;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <DisableSpecificWarnings>4996;4127</DisableSpecificWarnings>
       <CompileAsManaged>false</CompileAsManaged>
diff --git a/projects/vstudio/readme.txt b/projects/vstudio/readme.txt
index 2231f4a..2b4766f 100644
--- a/projects/vstudio/readme.txt
+++ b/projects/vstudio/readme.txt
@@ -1,7 +1,7 @@
 
 VisualStudio instructions
 
-libpng version 1.5.5beta05 - July 29, 2011
+libpng version 1.5.5beta05 - August 17, 2011
 
 Copyright (c) 1998-2010 Glenn Randers-Pehrson
 
diff --git a/projects/vstudio/zlib.props b/projects/vstudio/zlib.props
index 524b4dd..636b360 100644
--- a/projects/vstudio/zlib.props
+++ b/projects/vstudio/zlib.props
@@ -2,7 +2,7 @@
 <!--
  * zlib.props - location of zlib source
  *
- * libpng version 1.5.5beta05 - July 29, 2011
+ * libpng version 1.5.5beta05 - August 17, 2011
  *
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  *
diff --git a/projects/vstudio/zlib/zlib.vcxproj b/projects/vstudio/zlib/zlib.vcxproj
index aa125de..d627817 100644
--- a/projects/vstudio/zlib/zlib.vcxproj
+++ b/projects/vstudio/zlib/zlib.vcxproj
@@ -84,7 +84,7 @@
   </PropertyGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug Library|Win32'">
     <ClCompile>
-      <PreprocessorDefinitions>WIN32;_DEBUG;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_WINDOWS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
       <WarningLevel>TurnOffAllWarnings</WarningLevel>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
@@ -99,7 +99,7 @@
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
     <ClCompile>
-      <PreprocessorDefinitions>WIN32;_DEBUG;_WINDOWS;_USRDLL;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_WINDOWS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <WarningLevel>TurnOffAllWarnings</WarningLevel>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
       <Optimization>Disabled</Optimization>
@@ -156,7 +156,7 @@
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
     <ClCompile>
-      <PreprocessorDefinitions>WIN32;NDEBUG;_WINDOWS;_USRDLL;DEBUGZLIB_EXPORTS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_WINDOWS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <WarningLevel>Level3</WarningLevel>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
     </ClCompile>