diff --git a/skimage/exposure/unwrap_2d_ljmu.c b/skimage/exposure/unwrap_2d_ljmu.c
index 7ffcbeef..abc66451 100644
--- a/skimage/exposure/unwrap_2d_ljmu.c
+++ b/skimage/exposure/unwrap_2d_ljmu.c
@@ -17,13 +17,14 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
+
+#define PI M_PI
+#define TWOPI (2 * M_PI)
 
 //TODO: remove global variables
 //TODO: make thresholds independent
 
-static float PI = 3.141592654f;
-static float TWOPI = 6.283185307f;
-
 #define NOMASK 0
 #define MASK 1
 
diff --git a/skimage/exposure/unwrap_3d_ljmu.c b/skimage/exposure/unwrap_3d_ljmu.c
index b8a44a73..99800410 100644
--- a/skimage/exposure/unwrap_3d_ljmu.c
+++ b/skimage/exposure/unwrap_3d_ljmu.c
@@ -19,9 +19,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 
-static float PI = 3.141592654f;
-static float TWOPI = 6.283185307f;
+#define PI M_PI
+#define TWOPI (2 * M_PI)
 
 #define NOMASK 0
 #define MASK 1