diff --git a/devel/rgbds/Makefile b/devel/rgbds/Makefile
index 3b2808b14e35..c22edff49297 100644
--- a/devel/rgbds/Makefile
+++ b/devel/rgbds/Makefile
@@ -1,18 +1,24 @@
 PORTNAME=	rgbds
-DISTVERSION=	0.5.0
+DISTVERSION=	0.5.1
 CATEGORIES=	devel games
 MASTER_SITES=	https://github.com/gbdev/rgbds/releases/download/v${DISTVERSION}/
 
 MAINTAINER=	tobik@FreeBSD.org
 COMMENT=	Free assembler/linker for the Game Boy and Game Boy Color
 
 LICENSE=	MIT
 LICENSE_FILE=	${WRKSRC}/LICENSE
 
 LIB_DEPENDS=	libpng.so:graphics/png
 
 USES=		bison compiler:c11 dos2unix pkgconfig
 MAKE_ARGS=	Q= # verbose builds
 WRKSRC=		${WRKDIR}/rgbds
 
+do-configure:
+# yank _POSIX_C_SOURCE when there is no support for _ISOC11_SOURCE
+	@cd ${WRKSRC}; ${PRINTF} '#include <assert.h>\nint main(){static_assert(1, "");}' | \
+		${CC} -std=gnu11 -D_POSIX_C_SOURCE=200809L -D_ISOC11_SOURCE -xc - 2>/dev/null || \
+		${REINPLACE_CMD} 's,-D_POSIX_C_SOURCE=200809L,,' ${WRKSRC}/Makefile
+
 .include <bsd.port.mk>
diff --git a/devel/rgbds/distinfo b/devel/rgbds/distinfo
index 86f91d774cb5..0a2c2b62b913 100644
--- a/devel/rgbds/distinfo
+++ b/devel/rgbds/distinfo
@@ -1,3 +1,3 @@
-TIMESTAMP = 1618806421
-SHA256 (rgbds-0.5.0.tar.gz) = 56708515afafa8bf6e8e5aec398d23484859008da5714d2c160107626142964b
-SIZE (rgbds-0.5.0.tar.gz) = 7921624
+TIMESTAMP = 1620716695
+SHA256 (rgbds-0.5.1.tar.gz) = e42a4b6a7f45e5e6ebc56c513f5607c6adcccb1b7f44c0cb35fef428ed9cbe8c
+SIZE (rgbds-0.5.1.tar.gz) = 7938330
diff --git a/devel/rgbds/files/patch-Makefile b/devel/rgbds/files/patch-Makefile
deleted file mode 100644
index 7eb7ab8341d0..000000000000
--- a/devel/rgbds/files/patch-Makefile
+++ /dev/null
@@ -1,30 +0,0 @@
-In file included from src/asm/charmap.c:22:
-include/hashmap.h:18:15: error: expected parameter declarator
-static_assert(HALF_HASH_NB_BITS * 2 == HASH_NB_BITS, "");
-              ^
-include/hashmap.h:17:27: note: expanded from macro 'HALF_HASH_NB_BITS'
-#define HALF_HASH_NB_BITS 16
-                          ^
-include/hashmap.h:18:15: error: expected ')'
-include/hashmap.h:17:27: note: expanded from macro 'HALF_HASH_NB_BITS'
-#define HALF_HASH_NB_BITS 16
-                          ^
-include/hashmap.h:18:14: note: to match this '('
-static_assert(HALF_HASH_NB_BITS * 2 == HASH_NB_BITS, "");
-             ^
-include/hashmap.h:18:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
-static_assert(HALF_HASH_NB_BITS * 2 == HASH_NB_BITS, "");
-^
-1 warning and 2 errors generated.
-
---- Makefile.orig	2021-03-10 06:20:18 UTC
-+++ Makefile
-@@ -35,7 +35,7 @@ WARNFLAGS	:= -Wall
- # Overridable CFLAGS
- CFLAGS		?= -O3 -flto -DNDEBUG
- # Non-overridable CFLAGS
--REALCFLAGS	:= ${CFLAGS} ${WARNFLAGS} -std=gnu11 -D_POSIX_C_SOURCE=200809L \
-+REALCFLAGS	:= ${CFLAGS} ${WARNFLAGS} -std=gnu11 \
- 		   -Iinclude
- # Overridable LDFLAGS
- LDFLAGS		?=