diff --git a/src/modules/ekf2/EKF/covariance.cpp b/src/modules/ekf2/EKF/covariance.cpp
index dd2ce97cf6..5820fc74d7 100644
--- a/src/modules/ekf2/EKF/covariance.cpp
+++ b/src/modules/ekf2/EKF/covariance.cpp
@@ -296,10 +296,12 @@ void Ekf::constrainStateVar(const IdxDof &state, float min, float max)
 		} else if (P(i, i) > max) {
 			// Constrain the variance growth by fusing zero innovation as clipping the variance
 			// would artifically increase the correlation between states and destabilize the filter.
+			// constrain_variances=false prevents unbounded recursion via
+			// fuseDirectStateMeasurement -> constrainStateVariances -> constrainStateVar -> here.
 			const float innov = 0.f;
 			const float R = 10.f * P(i, i); // This reduces the variance by ~10% as K = P / (P + R)
 			const float innov_var = P(i, i) + R;
-			fuseDirectStateMeasurement(innov, innov_var, R, i);
+			fuseDirectStateMeasurement(innov, innov_var, R, i, /*constrain_variances=*/false);
 		}
 	}
 }
diff --git a/src/modules/ekf2/EKF/ekf.h b/src/modules/ekf2/EKF/ekf.h
index 5e36b1a1d5..8fa5834702 100644
--- a/src/modules/ekf2/EKF/ekf.h
+++ b/src/modules/ekf2/EKF/ekf.h
@@ -263,7 +263,10 @@ public:
 	}
 
 	// fuse single direct state measurement (eg NED velocity, NED position, mag earth field, etc)
-	void fuseDirectStateMeasurement(const float innov, const float innov_var, const float R, const int state_index);
+	// constrain_variances must be false when called from inside constrainStateVar to prevent
+	// unbounded recursion (constrainStateVariances can call back into this function).
+	void fuseDirectStateMeasurement(const float innov, const float innov_var, const float R, const int state_index,
+					bool constrain_variances = true);
 
 	bool measurementUpdate(VectorState &K, const VectorState &H, const float R, const float innovation);
 
diff --git a/src/modules/ekf2/EKF/ekf_helper.cpp b/src/modules/ekf2/EKF/ekf_helper.cpp
index 1ea83ceac8..381c10eca9 100644
--- a/src/modules/ekf2/EKF/ekf_helper.cpp
+++ b/src/modules/ekf2/EKF/ekf_helper.cpp
@@ -1027,7 +1027,8 @@ void Ekf::updateIMUBiasInhibit(const imuSample &imu_delayed)
 	}
 }
 
-void Ekf::fuseDirectStateMeasurement(const float innov, const float innov_var, const float R, const int state_index)
+void Ekf::fuseDirectStateMeasurement(const float innov, const float innov_var, const float R, const int state_index,
+				     bool constrain_variances)
 {
 	VectorState K;  // Kalman gain vector for any single observation - sequential fusion is used.
 
@@ -1081,7 +1082,9 @@ void Ekf::fuseDirectStateMeasurement(const float innov, const float innov_var, c
 
 #endif
 
-	constrainStateVariances();
+	if (constrain_variances) {
+		constrainStateVariances();
+	}
 
 	// apply the state corrections
 	fuse(K, innov);