diff --git a/pngwutil.c b/pngwutil.c
index 44ef005b4..de99afc36 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -678,6 +678,8 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
    png_ptr->zlib_text_method = 8;
 #endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
 
+   /* Free memory from previously opened zstream */
+   deflateEnd(&png_ptr->zstream);
    /* Initialize the zlib compressor */
    ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
        png_ptr->zlib_method, png_ptr->zlib_window_bits,
@@ -776,6 +778,9 @@ png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
       int ret;
       unsigned int z_cmf;  /* zlib compression method and flags */
 
+      /* Free memory from previously opened zstream */
+      deflateEnd(&png_ptr->zstream);
+
       ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
           png_ptr->zlib_method, png_ptr->zlib_window_bits,
           png_ptr->zlib_mem_level, png_ptr->zlib_strategy);