diff --git a/font-src/support/geometry.js b/font-src/support/geometry.js
index eb2984211..d207218c5 100644
--- a/font-src/support/geometry.js
+++ b/font-src/support/geometry.js
@@ -50,6 +50,9 @@ class ContourGeometry extends GeometryBase {
 		return !this.m_points.length;
 	}
 	measureComplexity() {
+		for (const z of this.m_points) {
+			if (!isFinite(z.x) || !isFinite(z.y)) return 0xffff;
+		}
 		return this.m_points.length;
 	}
 	toShapeStringOrNull() {
diff --git a/font-src/support/spiro-expand.js b/font-src/support/spiro-expand.js
index 74fef3fcc..5712f79be 100644
--- a/font-src/support/spiro-expand.js
+++ b/font-src/support/spiro-expand.js
@@ -157,10 +157,12 @@ class SpiroExpansionContext2 {
 		if (this.nKnotsProcessed === 1) {
 			const angle = computeNormalAngle(this.gizmo, arc.deriveX0, arc.deriveY0);
 			if (isFinite(angle)) this.controlKnots[0].normalAngle = angle;
+			else throw new Error("NaN angle detected.");
 		}
 		{
 			const angle = computeNormalAngle(this.gizmo, arc.deriveX1, arc.deriveY1);
 			if (isFinite(angle)) this.controlKnots[this.nKnotsProcessed].normalAngle = angle;
+			else throw new Error("NaN angle detected.");
 		}
 		this.nKnotsProcessed += 1;
 	}