diff --git a/ANNOUNCE b/ANNOUNCE
index 37a01a7..cc5019f 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -93,6 +93,14 @@
     the optimizations ('check' vs 'api') are exposed in the public header files
     except that the new setting PNG_ARM_NEON_OPT documents how libpng makes the
     decision about whether or not to use the optimizations.
+  Protect symbol prefixing against CC/CPPFLAGS/CFLAGS useage.
+    Previous iOS/Xcode fixes for the ARM NEON optimizations moved the test
+    on __ARM_NEON__ from configure time to compile time.  This breaks symbol
+    prefixing because the definition of the special png_init_filter_functions
+    call was hidden at configure time if the relevant compiler arguments are
+    passed in CFLAGS as opposed to CC.  This change attempts to avoid all
+    the confusion that would result by declaring the init function even when
+    it is not used, so that it will always get prefixed.
 
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diff --git a/CHANGES b/CHANGES
index 4615e2b..68ba609 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4577,6 +4577,14 @@
     the optimizations ('check' vs 'api') are exposed in the public header files
     except that the new setting PNG_ARM_NEON_OPT documents how libpng makes the
     decision about whether or not to use the optimizations.
+  Protect symbol prefixing against CC/CPPFLAGS/CFLAGS useage.
+    Previous iOS/Xcode fixes for the ARM NEON optimizations moved the test
+    on __ARM_NEON__ from configure time to compile time.  This breaks symbol
+    prefixing because the definition of the special png_init_filter_functions
+    call was hidden at configure time if the relevant compiler arguments are
+    passed in CFLAGS as opposed to CC.  This change attempts to avoid all
+    the confusion that would result by declaring the init function even when
+    it is not used, so that it will always get prefixed.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngpriv.h b/pngpriv.h
index c42aed7..9729dac 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -96,8 +96,16 @@
  * done and this interferes with the handling of the ARM NEON optimizations, and
  * possibly other similiar optimizations.  Put additional tests here; in general
  * this is needed when the same option can be changed at both compile time and
- * run time depending on the target OS (i.e. iOS vs Android.)  The changes have
- * to occur here to get the symbol prefixing to work consistently.
+ * run time depending on the target OS (i.e. iOS vs Android.)
+ *
+ * NOTE: symbol prefixing does not pass $(CFLAGS) to the preprocessor, because
+ * this is not possible with certain compilers (Oracle SUN OS CC), as a result
+ * it is necessary to ensure that all extern functions that *might* be used
+ * regardless of $(CFLAGS) get declared in this file.  The test on __ARM_NEON__
+ * below is one example of this behavior because it is controlled by the
+ * presence or not of -mfpu=neon on the GCC command line, it is possible to do
+ * this in $(CC), e.g. "CC=gcc -mfpu=neon", but people who build libpng rarely
+ * do this.
  */
 #ifndef PNG_ARM_NEON_OPT
    /* ARM NEON optimizations are being controlled by the compiler settings,
@@ -115,7 +123,7 @@
 
 #if PNG_ARM_NEON_OPT > 0
    /* NEON optimizations are to be at least considered by libpng, enable the
-    * callbacks to do this.  (This is what matters for the symbol prefixing.)
+    * callbacks to do this.
     */
 #  define PNG_FILTER_OPTIMIZATIONS png_init_filter_functions_neon
 #endif
@@ -1941,14 +1949,22 @@
 
 #endif /* SIMPLIFIED READ/WRITE */
 
+/* These are initialization functions for hardware specific PNG filter
+ * optimizations; list these here then select the appropriate one at compile
+ * time using the macro PNG_FILTER_OPTIMIZATIONS.  If the macro is not defined
+ * the generic code is used.
+ */
 #ifdef PNG_FILTER_OPTIMIZATIONS
 PNG_INTERNAL_FUNCTION(void, PNG_FILTER_OPTIMIZATIONS, (png_structp png_ptr,
-    unsigned int bpp), PNG_EMPTY);
-   /* This is the initialization function for hardware specific optimizations,
-    * one implementation (for ARM NEON machines) is contained in
-    * arm/filter_neon.c.  It need not be defined - the generic code will be used
-    * if not.
+   unsigned int bpp), PNG_EMPTY);
+   /* Just declare the optimization that will be used */
+#else
+   /* List *all* the possible optimizations here - this branch is required if
+    * the builder of libpng passes the definition of PNG_FILTER_OPTIMIZATIONS in
+    * CFLAGS in place of CPPFLAGS *and* uses symbol prefixing.
     */
+PNG_INTERNAL_FUNCTION(void, png_init_filter_functions_neon,
+   (png_structp png_ptr, unsigned int bpp), PNG_EMPTY);
 #endif
 
 /* Maintainer: Put new private prototypes here ^ */
diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
index ae9f323..4dea09c 100755
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -119,7 +119,7 @@
 #
 # If you create a private DLL you need to define the following
 # macros in the file 'pngusr.h' and set -DPNG_USER_CONFIG for
-# compilation (i.e. in CFLAGS.)
+# compilation (i.e. in CPPFLAGS.)
 # #define PNG_USER_PRIVATEBUILD \
 #     <Describes by whom and why this version of the DLL was built>
 #  e.g. #define PNG_USER_PRIVATEBUILD "Build by MyCompany for xyz reasons."
@@ -204,11 +204,11 @@
 #
 # ARM_NEON_OPT: unset: check at compile time (__ARM_NEON__ must be defined by
 #                      the compiler, typically as a result of specifying
-#                      -mfpu=neon on the command line.)
+#                      CC="gcc -mfpu=neon".)
 #                   0: disable (even if the CPU has a NEON FPU.)
 #                   1: check at run time (via ARM_NEON_{API,CHECK})
 #                   2: switch on unconditionally (inadvisable - instead pass
-#                      -mfpu=neon to GCC in CFLAGS)
+#                      -mfpu=neon to GCC in CC)
 #           When building libpng avoid using any setting other than '0'; '1' is
 #           set automatically when either 'API' or 'CHECK' are configured in,
 #           '2' should not be necessary as -mfpu=neon will achieve the same