diff --git a/ANNOUNCE b/ANNOUNCE
index b8e9ce8bb..7f9a92db4 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -538,6 +538,7 @@ Version 1.6.0beta31 [October 26, 2012]
     has been changed to allow an external CMS to be used.  This code is
     temporarily disabled until a suitable set of test cases using one or more
     external CMS implementations have been implemented.
+  Make builds -DPNG_NO_READ_GAMMA compile (the unit tests still fail).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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diff --git a/CHANGES b/CHANGES
index 58cbd10ef..2ff5e7eea 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4290,6 +4290,7 @@ Version 1.6.0beta31 [October 26, 2012]
     has been changed to allow an external CMS to be used.  This code is
     temporarily disabled until a suitable set of test cases using one or more
     external CMS implementations have been implemented.
+  Make builds -DPNG_NO_READ_GAMMA compile (the unit tests still fail).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/contrib/libtests/pngvalid.c b/contrib/libtests/pngvalid.c
index 7d39161a8..9edae396b 100644
--- a/contrib/libtests/pngvalid.c
+++ b/contrib/libtests/pngvalid.c
@@ -2004,6 +2004,7 @@ static double abserr(PNG_CONST png_modifier *pm, int in_depth, int out_depth)
       return pm->maxabs8;
 }
 
+#ifdef PNG_READ_GAMMA_SUPPORTED
 static double calcerr(PNG_CONST png_modifier *pm, int in_depth, int out_depth)
 {
    /* Error in the linear composition arithmetic - only relevant when
@@ -2120,6 +2121,7 @@ static int output_quantization_factor(PNG_CONST png_modifier *pm, int in_depth,
    else
       return 1;
 }
+#endif /* PNG_READ_GAMMA_SUPPORTED */
 
 /* One modification structure must be provided for each chunk to be modified (in
  * fact more than one can be provided if multiple separate changes are desired
@@ -2808,6 +2810,7 @@ srgb_modification_init(srgb_modification *me, png_modifier *pm, png_byte intent)
    pm->modifications = &me->this;
 }
 
+#ifdef PNG_READ_GAMMA_SUPPORTED
 typedef struct sbit_modification
 {
    png_modification this;
@@ -2874,6 +2877,7 @@ sbit_modification_init(sbit_modification *me, png_modifier *pm, png_byte sbit)
    me->this.next = pm->modifications;
    pm->modifications = &me->this;
 }
+#endif /* PNG_READ_GAMMA_SUPPORTED */
 #endif /* PNG_READ_TRANSFORMS_SUPPORTED */
 
 /***************************** STANDARD PNG FILES *****************************/
diff --git a/pngrtran.c b/pngrtran.c
index 33a1d23fc..c67298357 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -3284,7 +3284,7 @@ png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
 
       if (row_info->bit_depth == 8)
       {
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
          /* Notice that gamma to/from 1 are not necessarily inverses (if
           * there is an overall gamma correction).  Prior to 1.5.5 this code
           * checked the linearized values for equality; this doesn't match
@@ -3361,7 +3361,7 @@ png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
 
       else /* RGB bit_depth == 16 */
       {
-#if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
+#ifdef PNG_READ_GAMMA_SUPPORTED
          if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
          {
             png_bytep sp = row;
@@ -3535,12 +3535,12 @@ png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
    png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
    png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
    int gamma_shift = png_ptr->gamma_shift;
+   int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
 #endif
 
    png_bytep sp;
    png_uint_32 i;
    png_uint_32 row_width = row_info->width;
-   int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
    int shift;
 
    png_debug(1, "in png_do_compose");