diff --git a/gtsam/linear/NoiseModel.cpp b/gtsam/linear/NoiseModel.cpp
index 80210c3b7..e539d9579 100644
--- a/gtsam/linear/NoiseModel.cpp
+++ b/gtsam/linear/NoiseModel.cpp
@@ -807,7 +807,10 @@ GemanMcClure::GemanMcClure(double c, const ReweightScheme reweight)
 }
 
 double GemanMcClure::weight(double error) const {
-  return c_/(c_ + error*error);
+  const double c2 = c_*c_;
+  const double c4 = c2*c2;
+  const double c2error = c2 + error*error;
+  return c4/(c2error*c2error);
 }
 
 void GemanMcClure::print(const std::string &s="") const {
diff --git a/gtsam/linear/NoiseModel.h b/gtsam/linear/NoiseModel.h
index 25b34ce18..db01152f6 100644
--- a/gtsam/linear/NoiseModel.h
+++ b/gtsam/linear/NoiseModel.h
@@ -827,7 +827,8 @@ namespace gtsam {
       /// (Zhang97ivc).
       ///
       /// Note that Geman-McClure weight function uses the parameter c == 1.0,
-      /// but here it's allowed to use different values.
+      /// but here it's allowed to use different values, so we actually have
+      /// the generalized Geman-McClure from (Agarwal15phd).
       class GTSAM_EXPORT GemanMcClure : public Base {
       public:
         typedef boost::shared_ptr<GemanMcClure> shared_ptr;
diff --git a/gtsam/linear/tests/testNoiseModel.cpp b/gtsam/linear/tests/testNoiseModel.cpp
index c1e9d95f6..01f653d73 100644
--- a/gtsam/linear/tests/testNoiseModel.cpp
+++ b/gtsam/linear/tests/testNoiseModel.cpp
@@ -338,8 +338,8 @@ TEST(NoiseModel, robustFunctionGemanMcClure)
   const mEstimator::GemanMcClure::shared_ptr gmc = mEstimator::GemanMcClure::Create(k);
   const double weight1 = gmc->weight(error1),
                weight2 = gmc->weight(error2);
-  DOUBLES_EQUAL(0.5       , weight1, 1e-8);
-  DOUBLES_EQUAL(0.00990099, weight2, 1e-8);
+  DOUBLES_EQUAL(0.25      , weight1, 1e-8);
+  DOUBLES_EQUAL(9.80296e-5, weight2, 1e-8);
 }
 
 TEST(NoiseModel, robustFunctionDCS)
@@ -385,8 +385,12 @@ TEST(NoiseModel, robustNoiseGemanMcClure)
 
   robust->WhitenSystem(A, b);
 
-  const double sqrt_weight_error1 = sqrt(0.5);
-  const double sqrt_weight_error2 = sqrt(k/(k + error2*error2));
+  const double k2 = k*k;
+  const double k4 = k2*k2;
+  const double k2error = k2 + error2*error2;
+
+  const double sqrt_weight_error1 = sqrt(0.25);
+  const double sqrt_weight_error2 = sqrt(k4/(k2error*k2error));
 
   DOUBLES_EQUAL(sqrt_weight_error1*error1, b(0), 1e-8);
   DOUBLES_EQUAL(sqrt_weight_error2*error2, b(1), 1e-8);