diff --git a/contrib/poly2tri/poly2tri/common/utils.h b/contrib/poly2tri/poly2tri/common/utils.h
index cb7a7dc01..f123fedaf 100644
--- a/contrib/poly2tri/poly2tri/common/utils.h
+++ b/contrib/poly2tri/poly2tri/common/utils.h
@@ -32,15 +32,13 @@
 #ifndef UTILS_H
 #define UTILS_H
 
-// Otherwise #defines like M_PI are undeclared under Visual Studio
-#define _USE_MATH_DEFINES
-
 #include <exception>
-#include <math.h>
 
 namespace p2t {
 
-const double PI_3div4 = 3 * M_PI / 4;
+const double PI = 3.1415926535897932384626433832795029;
+const double PI_2 = 2 * PI;
+const double PI_3div4 = 3 * PI / 4;
 const double EPSILON = 1e-15;
 
 enum Orientation { CW, CCW, COLLINEAR };
diff --git a/contrib/poly2tri/poly2tri/sweep/sweep.cc b/contrib/poly2tri/poly2tri/sweep/sweep.cc
index 0f398ad2d..f60e0d7a8 100644
--- a/contrib/poly2tri/poly2tri/sweep/sweep.cc
+++ b/contrib/poly2tri/poly2tri/sweep/sweep.cc
@@ -231,7 +231,7 @@ void Sweep::FillAdvancingFront(SweepContext& tcx, Node& n)
 
   while (node->next) {
     double angle = HoleAngle(*node);
-    if (angle > M_PI_2 || angle < -M_PI_2) break;
+    if (angle > PI || angle < -PI_2) break;
     Fill(tcx, *node);
     node = node->next;
   }
@@ -241,7 +241,7 @@ void Sweep::FillAdvancingFront(SweepContext& tcx, Node& n)
 
   while (node->prev) {
     double angle = HoleAngle(*node);
-    if (angle > M_PI_2 || angle < -M_PI_2) break;
+    if (angle > PI_2 || angle < -PI_2) break;
     Fill(tcx, *node);
     node = node->prev;
   }