diff --git a/Makefile b/Makefile
index 274e2d4..42404e7 100644
--- a/Makefile
+++ b/Makefile
@@ -14,9 +14,10 @@ endif
 SRC_C   = $(wildcard src/*.c)
 SRC_CXX = $(wildcard src/*.cpp)
 
-INCLUDE=include src/internal
+INCLUDE=include
+INCLUDE_INTERNAL=src/internal
 
-COMMON_FLAGS= -W -Wall -Wextra -Wstrict-aliasing -fno-strict-aliasing "-D_VERSION=$(VERSION)" $(addprefix -I,$(INCLUDE))
+COMMON_FLAGS= -W -Wall -Wextra -Wstrict-aliasing -fno-strict-aliasing "-D_VERSION=$(VERSION)" $(addprefix -I,$(INCLUDE)) $(addprefix -I,$(INCLUDE_INTERNAL))
 
 TARGET_CPU?=native
 OPT_FLAGS?= $(addprefix -march=,$(TARGET_CPU)) -fgraphite -fopenmp -floop-parallelize-all -ftree-parallelize-loops=4 \