diff --git a/png.h b/png.h
index 457c932..861e84b 100644
--- a/png.h
+++ b/png.h
@@ -3204,9 +3204,12 @@
 #ifdef PNG_MIPS_MSA_API_SUPPORTED
 #  define PNG_MIPS_MSA   6 /* HARDWARE: MIPS Msa SIMD instructions supported */
 #endif
-#define PNG_IGNORE_ADLER32 8
+#ifdef PNG_DISABLE_ADLER32_CHECK_SUPPORTED
+#  define PNG_IGNORE_ADLER32 8 /* SOFTWARE: disable Adler32 check on IDAT */
+#endif
 #ifdef PNG_POWERPC_VSX_API_SUPPORTED
-#  define PNG_POWERPC_VSX   10 /* HARDWARE: PowerPC VSX SIMD instructions supported */
+#  define PNG_POWERPC_VSX   10 /* HARDWARE: PowerPC VSX SIMD instructions
+                                * supported */
 #endif
 #ifdef PNG_MIPS_MMI_API_SUPPORTED
 #  define PNG_MIPS_MMI   12 /* HARDWARE: MIPS MMI SIMD instructions supported */
diff --git a/pngrutil.c b/pngrutil.c
index 068ab19..f471215 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -421,8 +421,7 @@
             png_ptr->flags |= PNG_FLAG_ZSTREAM_INITIALIZED;
       }
 
-#if ZLIB_VERNUM >= 0x1290 && \
-   defined(PNG_SET_OPTION_SUPPORTED) && defined(PNG_IGNORE_ADLER32)
+#ifdef PNG_DISABLE_ADLER32_CHECK_SUPPORTED
       if (((png_ptr->options >> PNG_IGNORE_ADLER32) & 3) == PNG_OPTION_ON)
          /* Turn off validation of the ADLER32 checksum in IDAT chunks */
          ret = inflateValidate(&png_ptr->zstream, 0);
diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
index f4d14a2..739805d 100644
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -385,6 +385,34 @@
 option BENIGN_WRITE_ERRORS requires BENIGN_ERRORS disabled
 option BENIGN_READ_ERRORS requires BENIGN_ERRORS
 
+# Adler32 checksum
+#
+# This option allows the check of the Adler32 checksum performed by zlib to
+# be turned off for IDAT chunks (only).  Unless this option is enabled and
+# turned on (not the default even if enabled) a failed Adler32 at the end of the
+# stream will result in a decompression (inflate) failure on read even though
+# the entire image might have been read successfully.
+#
+# This option relies on an undocumented function 'inflateValidate' which is
+# present in only some versions of zlib.  If the function is not present in the
+# zlib used with libpng code which uses -lpng is likely to fail to link or to
+# launch in the case of a DLL.
+#
+# Therefore this option is currently disabled by default; it has to be turned on
+# in pngusr.dfa and then the application program has to explicitly turn the
+# functionality on by calling png_set_option.
+#
+# Furthermore the option is explicitly turned off here if the zlib version
+# number is below that required - libpng wouldn't compile in that case if the
+# option were turned on.
+option DISABLE_ADLER32_CHECK requires READ enables SET_OPTION disabled
+
+# ZLIB_VERNUM must be used here, not PNG_ZLIB_VERNUM, because
+# scripts/options.awk ends up putting this test adhead of the setting of
+# PNG_ZLIB_VERNUM (apparently above, but not because of the two-pass processing)
+@#if ZLIB_VERNUM < 0x1290
+@#   define PNG_NO_DISABLE_ADLER32_CHECK
+@#endif
 
 # Generic options - affect both read and write.
 
diff --git a/scripts/pnglibconf.h.prebuilt b/scripts/pnglibconf.h.prebuilt
index 06ecdd6..06d6045 100644
--- a/scripts/pnglibconf.h.prebuilt
+++ b/scripts/pnglibconf.h.prebuilt
@@ -1,3 +1,4 @@
+/* 1.6.41.git STANDARD API DEFINITION */
 /* pnglibconf.h - library build configuration */
 
 /* libpng version 1.6.41.git */
@@ -27,6 +28,7 @@
 #define PNG_COLORSPACE_SUPPORTED
 #define PNG_CONSOLE_IO_SUPPORTED
 #define PNG_CONVERT_tIME_SUPPORTED
+/*#undef PNG_DISABLE_ADLER32_CHECK_SUPPORTED*/
 #define PNG_EASY_ACCESS_SUPPORTED
 /*#undef PNG_ERROR_NUMBERS_SUPPORTED*/
 #define PNG_ERROR_TEXT_SUPPORTED