diff --git a/Lib/fontTools/varLib/instancer/solver.py b/Lib/fontTools/varLib/instancer/solver.py
index ba1faf731..468f04277 100644
--- a/Lib/fontTools/varLib/instancer/solver.py
+++ b/Lib/fontTools/varLib/instancer/solver.py
@@ -102,7 +102,7 @@ def _solve(tent, axisLimit, negative=False):
         # Crossing point on the axis.
         crossing = peak + ((1 - gain) * (upper - peak) / (1 - outGain))
 
-        loc = (peak, peak, crossing)
+        loc = (axisDef, peak, crossing)
         scalar = 1
 
         # The part before the crossing point.
diff --git a/Tests/varLib/instancer/solver_test.py b/Tests/varLib/instancer/solver_test.py
index 58114d22c..241a824cb 100644
--- a/Tests/varLib/instancer/solver_test.py
+++ b/Tests/varLib/instancer/solver_test.py
@@ -218,6 +218,18 @@ class RebaseTentTest(object):
                     (1, (0, 0.4, 1.99994)),
                 ],
             ),
+            # https://github.com/fonttools/fonttools/issues/3139
+            pytest.param(
+                (0, 0.5, 1),
+                (-1, 0.25, 1),
+                [
+                    (0.5, None),
+                    (0.5, (0.0, 1 / 3, 2 / 3)),
+                    (-0.5, (2 / 3, 1, 1)),
+                    (-0.5, (-1, -0.2, 0)),
+                    (-0.5, (-1, -1, -0.2)),
+                ],
+            ),
             # Dirac delta at new default. Fancy!
             pytest.param(
                 (0.5, 0.5, 0.5),
@@ -233,7 +245,6 @@ class RebaseTentTest(object):
         ],
     )
     def test_rebaseTent(self, tent, axisRange, expected):
-
         sol = solver.rebaseTent(tent, axisRange)
 
         a = pytest.approx