diff --git a/misc/mnn/Makefile b/misc/mnn/Makefile
index 720287223ee5..86dbda3af2fa 100644
--- a/misc/mnn/Makefile
+++ b/misc/mnn/Makefile
@@ -12,9 +12,10 @@ LICENSE=	APACHE20
 
 BROKEN_i386=	always_inline function '_mm_set1_ps' requires target feature 'sse', but would be inlined into function 'Vec4' that is compiled without support for 'sse'
 
-BUILD_DEPENDS=	bash:shells/bash
+BUILD_DEPENDS=	bash:shells/bash \
+		flatc:devel/flatbuffers
 
-USES=		cmake compiler:c++11-lang shebangfix
+USES=		cmake compiler:c++11-lang localbase shebangfix
 USE_GITHUB=	yes
 GH_ACCOUNT=	alibaba
 GH_PROJECT=	MNN
@@ -49,7 +50,7 @@ CMAKE_ARGS+=	-DMNN_USE_AVX:BOOL=OFF \
 .endif
 
 pre-build: # https://github.com/alibaba/MNN/issues/648
-	@cd ${WRKSRC}/schema && ./generate.sh
+	@cd ${WRKSRC}/schema && FREEBSD_FLATC=${LOCALBASE}/bin/flatc ./generate.sh
 
 do-install-APPS-on:
 .for f in	MNNConvert MNNV2Basic.out mobilenetTest.out backendTest.out testModel.out testModelWithDescrisbe.out getPerformance.out checkInvalidValue.out timeProfile.out quantized.out \
diff --git a/misc/mnn/files/patch-CMakeLists.txt b/misc/mnn/files/patch-CMakeLists.txt
new file mode 100644
index 000000000000..d690a6beaf55
--- /dev/null
+++ b/misc/mnn/files/patch-CMakeLists.txt
@@ -0,0 +1,10 @@
+--- CMakeLists.txt.orig	2020-09-20 17:36:43 UTC
++++ CMakeLists.txt
+@@ -268,7 +268,6 @@ include_directories(${CMAKE_CURRENT_LIST_DIR}/include/
+                     ${CMAKE_CURRENT_LIST_DIR}/source/
+                     ${CMAKE_CURRENT_LIST_DIR}/schema/current/
+                     ${CMAKE_CURRENT_LIST_DIR}/3rd_party/
+-                    ${CMAKE_CURRENT_LIST_DIR}/3rd_party/flatbuffers/include
+                     ${CMAKE_CURRENT_LIST_DIR}/3rd_party/half
+                     ${CMAKE_CURRENT_LIST_DIR}/3rd_party/imageHelper
+                     ${CMAKE_CURRENT_LIST_DIR}/3rd_party/OpenCLHeaders/
diff --git a/misc/mnn/files/patch-schema_generate.sh b/misc/mnn/files/patch-schema_generate.sh
new file mode 100644
index 000000000000..b1cce451b952
--- /dev/null
+++ b/misc/mnn/files/patch-schema_generate.sh
@@ -0,0 +1,20 @@
+--- schema/generate.sh.orig	2020-09-20 17:43:01 UTC
++++ schema/generate.sh
+@@ -9,7 +9,7 @@ if [[ "$1" == "-lazy" ]] && [[ -d current ]]; then
+ fi
+ 
+ # check is flatbuffer installed or not
+-FLATC=../3rd_party/flatbuffers/tmp/flatc
++FLATC=${FREEBSD_FLATC}
+ if [ ! -e $FLATC ]; then
+   echo "*** building flatc ***"
+ 
+@@ -39,7 +39,7 @@ rm -f current/*.h
+ # flatc all fbs
+ pushd current > /dev/null
+ echo "*** generating fbs under $DIR ***"
+-find ../$DIR/*.fbs | xargs ../$FLATC -c -b --gen-object-api --reflect-names
++find ../$DIR/*.fbs | xargs $FLATC -c -b --gen-object-api --reflect-names
+ popd > /dev/null
+ 
+ # finish