diff --git a/native/WDS/Makefile b/native/WDS/Makefile
index 258d550..506e2d5 100644
--- a/native/WDS/Makefile
+++ b/native/WDS/Makefile
@@ -1,7 +1,7 @@
 CC = gcc
 SRC_DIR = src
 SOURCE = $(SRC_DIR)/main.c $(SRC_DIR)/models.c $(SRC_DIR)/moeaframework.c
-C_FLAGS = -I$(SRC_DIR)/epanet2 -Lbin -lepanet2 -Wl,-R,\.
+C_FLAGS = -I$(SRC_DIR)/epanet2 -Lbin -lm -lepanet2 -Wl,-R,\.
 
 all:
 	$(MAKE) -C $(SRC_DIR)/epanet2
diff --git a/native/WDS/src/models.h b/native/WDS/src/models.h
index b267431..cf2b91d 100644
--- a/native/WDS/src/models.h
+++ b/native/WDS/src/models.h
@@ -1,5 +1,5 @@
-int nvars;
-int nobjs;
-int nconstrs;
-char* inputFile;
+extern int nvars;
+extern int nobjs;
+extern int nconstrs;
+extern char* inputFile;
 void test_problem (double *xreal, double *xbin, int **gene, double *obj, double *constr);
\ No newline at end of file