diff --git a/corelib/src/odometry/OdometryF2M.cpp b/corelib/src/odometry/OdometryF2M.cpp
index 7b62cad4..dc5ab044 100644
--- a/corelib/src/odometry/OdometryF2M.cpp
+++ b/corelib/src/odometry/OdometryF2M.cpp
@@ -1469,6 +1469,25 @@ Transform OdometryF2M::computeTransform(
 						}
 					}
 
+					const int scanMaxPoints = lastFrame_->sensorData().laserScanRaw().maxPoints();
+					if(frameValid && scanMaxPoints > 0)
+					{
+						float correspondenceRatio = Parameters::defaultIcpCorrespondenceRatio();
+						Parameters::parse(parameters_, Parameters::kIcpCorrespondenceRatio(), correspondenceRatio);
+						if(float(lastFrame_->sensorData().laserScanRaw().size()) <
+								float(scanMaxPoints) * correspondenceRatio)
+						{
+							UWARN("Scan has %d points of the %d of a full sweep, under the %s=%f "
+									"that a registration against it would have to reach, so no "
+									"later scan could be matched to it. Not initializing on it.",
+									(int)lastFrame_->sensorData().laserScanRaw().size(),
+									scanMaxPoints,
+									Parameters::kIcpCorrespondenceRatio().c_str(),
+									correspondenceRatio);
+							frameValid = false;
+						}
+					}
+
 					if(frameValid)
 					{
 						if (scanMapMaxRange_ > 0 ){
diff --git a/corelib/test/test_odometry.cpp b/corelib/test/test_odometry.cpp
index b39eda77..d1efe483 100644
--- a/corelib/test/test_odometry.cpp
+++ b/corelib/test/test_odometry.cpp
@@ -543,3 +543,44 @@ TEST_P(OdometryStrategyTest, IcpConvergesFromOffsetGuess)
 			<< guess.prettyPrint() << "); ICP did not converge";
 	expectPoseNear(pose, motion, 0.002f, 0.2f, "2D corner, offset guess");
 }
+
+// A sweep that arrives far short of the points it should have cannot be
+// registered against: Icp/CorrespondenceRatio is measured against a full sweep,
+// so even matching every point it does have would leave it under the ratio.
+// F2M refuses such a scan as the first keyframe rather than starting a map that
+// nothing can be matched to. maxPoints is what says how big a full sweep is, so
+// the check is only possible when a driver reported it.
+TEST(OdometryTest, RefusesAFirstScanTooSmallForTheCorrespondenceRatio)
+{
+	const ParametersMap parameters =
+			icpOdometryParameters(Odometry::kTypeF2M, /*force3DoF=*/false, /*guessMotion=*/false);
+	const LaserScan corner = makeCorner3D();   // 1200 points
+
+	// The same points three ways. First as a twentieth of the sweep they should be,
+	// which no registration could reach the 0.1 ratio against.
+	const LaserScan tooFewPoints(
+			corner.data(), 20*(int)corner.size(), /*maxRange=*/0.0f, corner.format());
+	std::unique_ptr<Odometry> refusing(Odometry::create(parameters));
+	ASSERT_TRUE(refusing.get() != 0);
+	SensorData refusingData = makeScanData(tooFewPoints, 1, 0.0);
+	EXPECT_TRUE(refusing->process(refusingData).isNull())
+			<< "a map was started on a scan no later one could be registered to";
+
+	// Then as everything a sweep has, which is what a full one looks like.
+	const LaserScan wholeSweep(
+			corner.data(), (int)corner.size(), /*maxRange=*/0.0f, corner.format());
+	std::unique_ptr<Odometry> accepting(Odometry::create(parameters));
+	ASSERT_TRUE(accepting.get() != 0);
+	SensorData acceptingData = makeScanData(wholeSweep, 1, 0.0);
+	EXPECT_FALSE(accepting->process(acceptingData).isNull())
+			<< "a full sweep was refused as the first keyframe";
+
+	// And last as makeCorner3D() builds it, with maxPoints left at 0: a driver that
+	// never said how big a sweep is, so there is no ratio to fall under and the check
+	// does not apply.
+	std::unique_ptr<Odometry> unchecked(Odometry::create(parameters));
+	ASSERT_TRUE(unchecked.get() != 0);
+	SensorData uncheckedData = makeScanData(corner, 1, 0.0);
+	EXPECT_FALSE(unchecked->process(uncheckedData).isNull())
+			<< "a scan of unknown sweep size was refused";
+}