diff --git a/ext/gd/gd_ctx.c b/ext/gd/gd_ctx.c
index d1ec8e0c25c..6fb7b84ce4d 100644
--- a/ext/gd/gd_ctx.c
+++ b/ext/gd/gd_ctx.c
@@ -24,8 +24,13 @@
 
 static void _php_image_output_putc(struct gdIOCtx *ctx, int c)
 {
+	/* without the following downcast, the write will fail
+	 * (i.e., will write a zero byte) for all
+	 * big endian architectures:
+	 */
+	unsigned char ch = (unsigned char) c;
 	TSRMLS_FETCH();
-	php_write(&c, 1 TSRMLS_CC);
+	php_write(&ch, 1 TSRMLS_CC);
 }
 
 static int _php_image_output_putbuf(struct gdIOCtx *ctx, const void* buf, int l)