diff --git a/Makefile b/Makefile
index 6133446..c242dc2 100644
--- a/Makefile
+++ b/Makefile
@@ -37,7 +37,9 @@ C_FLAGS += -fpic
 
 C_FLAGS += -O0 -g -Wall -Wextra -Werror
 CPP_FLAGS += $(addprefix -I, $(INCLUDES))
-CHECK_FLAGS = --enable=all --template=gcc --error-exitcode=1 --suppress=missingIncludeSystem --inline-suppr --force
+
+CHECK_FLAGS = $(addprefix -I,$(filter-out $(PREFIX)/include/,$(INCLUDES)))
+CHECK_FLAGS += --enable=all --template=gcc --error-exitcode=1 --suppress=missingIncludeSystem --inline-suppr --force
 
 C_SRCS = $(wildcard $(SRC_DIR)/*.c)
 C_OBJS = $(patsubst $(SRC_DIR)%,$(OBJ_DIR)%,$(patsubst %.c,%.o,$(C_SRCS)))
@@ -106,7 +108,7 @@ exec_unit_test: $(UNIT_TEST_TARGET)
 
 .PHONY: check
 check: $(C_SRCS)
-	$(CHECK) $(CPP_FLAGS) $(CHECK_FLAGS) $(C_SRCS)
+	$(CHECK) $(CHECK_FLAGS) $(C_SRCS)
 
 $(UNIT_TEST_TARGET): $(UNIT_TEST_OBJS) $(THIS_MAKEFILE)
 	@mkdir -p $(BIN_DIR)/$(UNIT_TEST_SRC_DIR)
diff --git a/src/i2c.c b/src/i2c.c
index 8748063..8e8e56e 100644
--- a/src/i2c.c
+++ b/src/i2c.c
@@ -40,6 +40,7 @@ int i2c_close(const struct i2c_bb *i2c)
     return res;
 }
 
+// cppcheck-suppress unusedFunction
 int i2c_read(const struct i2c_bb *i2c, uint8_t slave_addr, char *buffer, unsigned int len)
 {
     unsigned int i;
@@ -59,6 +60,7 @@ int i2c_read(const struct i2c_bb *i2c, uint8_t slave_addr, char *buffer, unsigne
     return (int)i;
 }
 
+// cppcheck-suppress unusedFunction
 int i2c_write(const struct i2c_bb *i2c, uint8_t slave_addr, const char *buffer, unsigned int len)
 {
     unsigned int i;
@@ -79,8 +81,6 @@ int i2c_write(const struct i2c_bb *i2c, uint8_t slave_addr, const char *buffer,
     return (int)i;
 }
 
-
-// cppcheck-suppress unusedFunction
 static void start_condition(const struct i2c_bb *i2c)
 {
     assert( NULL != i2c);
@@ -94,7 +94,6 @@ static void start_condition(const struct i2c_bb *i2c)
     usleep(5);
 }
 
-// cppcheck-suppress unusedFunction
 static void stop_condition(const struct i2c_bb *i2c)
 {
     assert( NULL != i2c);
@@ -107,7 +106,6 @@ static void stop_condition(const struct i2c_bb *i2c)
     usleep(5);
 }
 
-// cppcheck-suppress unusedFunction
 static bool write_byte(const struct i2c_bb *i2c, uint8_t byte)
 {
     uint8_t ack, i;
@@ -124,7 +122,6 @@ static bool write_byte(const struct i2c_bb *i2c, uint8_t byte)
     return (bool)(ack & 0x01);
 }
 
-// cppcheck-suppress unusedFunction
 static uint8_t read_byte(const struct i2c_bb *i2c, bool ack)
 {
     uint8_t res = 0, i;