diff --git a/cpp/Pose2.cpp b/cpp/Pose2.cpp
index 574fc0d20..9ffec1a18 100644
--- a/cpp/Pose2.cpp
+++ b/cpp/Pose2.cpp
@@ -153,7 +153,7 @@ namespace gtsam {
 
   	// Calculate delta rotation = between(R1,R2)
 		double c = c1 * c2 + s1 * s2, s = -s1 * c2 + c1 * s2;
-    Rot2 R(Rot2::fromCosSin(c,s));
+    Rot2 R(Rot2::atan2(s,c)); // normalizes
 
   	// Calculate delta translation = unrotate(R1, dt);
 		Point2 dt = p2.t() - p1.t();
diff --git a/cpp/Pose2.h b/cpp/Pose2.h
index 111a2db4c..11189dc9c 100644
--- a/cpp/Pose2.h
+++ b/cpp/Pose2.h
@@ -52,7 +52,7 @@ namespace gtsam {
 
     /** Constructor from 3*3 matrix */
     Pose2(const Matrix &T) :
-      r_(Rot2::fromCosSin(T(0, 0), T(1, 0))), t_(T(0, 2), T(1, 2)) {}
+      r_(Rot2::atan2(T(1, 0), T(0, 0))), t_(T(0, 2), T(1, 2)) {}
 
     /** print with optional string */
     void print(const std::string& s = "") const;