diff --git a/libpng-manual.txt b/libpng-manual.txt
index d19ac94e8..b19f099c8 100644
--- a/libpng-manual.txt
+++ b/libpng-manual.txt
@@ -2295,11 +2295,11 @@ with zlib) for details on the compression levels.
 
     #include zlib.h
 
-    /* set the zlib compression level */
+    /* Set the zlib compression level */
     png_set_compression_level(png_ptr,
         Z_BEST_COMPRESSION);
 
-    /* set other zlib parameters */
+    /* Set other zlib parameters for compressing IDAT */
     png_set_compression_mem_level(png_ptr, 8);
     png_set_compression_strategy(png_ptr,
         Z_DEFAULT_STRATEGY);
@@ -2307,7 +2307,10 @@ with zlib) for details on the compression levels.
     png_set_compression_method(png_ptr, 8);
     png_set_compression_buffer_size(png_ptr, 8192)
 
-    /* set zlib parameters for text compression */
+    /* Set zlib parameters for text compression
+     * If you don't call these, the parameters
+     * fall back on those defined for IDAT chunks
+     */
     png_set_text_compression_mem_level(png_ptr, 8);
     png_set_text_compression_strategy(png_ptr,
         Z_DEFAULT_STRATEGY);
diff --git a/libpng.3 b/libpng.3
index 98ad76e21..409ae291b 100644
--- a/libpng.3
+++ b/libpng.3
@@ -3238,11 +3238,11 @@ with zlib) for details on the compression levels.
 
     #include zlib.h
 
-    /* set the zlib compression level */
+    /* Set the zlib compression level */
     png_set_compression_level(png_ptr,
         Z_BEST_COMPRESSION);
 
-    /* set other zlib parameters */
+    /* Set other zlib parameters for compressing IDAT */
     png_set_compression_mem_level(png_ptr, 8);
     png_set_compression_strategy(png_ptr,
         Z_DEFAULT_STRATEGY);
@@ -3250,7 +3250,10 @@ with zlib) for details on the compression levels.
     png_set_compression_method(png_ptr, 8);
     png_set_compression_buffer_size(png_ptr, 8192)
 
-    /* set zlib parameters for text compression */
+    /* Set zlib parameters for text compression
+     * If you don't call these, the parameters
+     * fall back on those defined for IDAT chunks
+     */
     png_set_text_compression_mem_level(png_ptr, 8);
     png_set_text_compression_strategy(png_ptr,
         Z_DEFAULT_STRATEGY);