diff --git a/package/libs/mbedtls/Makefile b/package/libs/mbedtls/Makefile
index 8e0a480e40..19db4b803b 100644
--- a/package/libs/mbedtls/Makefile
+++ b/package/libs/mbedtls/Makefile
@@ -64,9 +64,9 @@ endef
 PKG_INSTALL:=1
 
 TARGET_CFLAGS += -ffunction-sections -fdata-sections
+TARGET_CFLAGS := $(filter-out -O%,$(TARGET_CFLAGS))
 
 CMAKE_OPTIONS += \
-	-DCMAKE_BUILD_TYPE:String="Release" \
 	-DUSE_SHARED_MBEDTLS_LIBRARY:Bool=ON \
 	-DENABLE_TESTING:Bool=OFF \
 	-DENABLE_PROGRAMS:Bool=ON