diff --git a/src/internal/fuzz/encoding_test.go b/src/internal/fuzz/encoding_test.go
index 4b55892acd..3a614f5bd2 100644
--- a/src/internal/fuzz/encoding_test.go
+++ b/src/internal/fuzz/encoding_test.go
@@ -104,6 +104,12 @@ float32(2.5)`,
 			ok: true,
 		},
 		{
+			// The two IEEE 754 bit patterns used for the math.Float{64,32}frombits
+			// encodings are non-math.NAN quiet-NaN values. Since they are not equal
+			// to math.NaN(), they should be re-encoded to their bit patterns. They
+			// are, respectively:
+			//   * math.Float64bits(math.NaN())+1
+			//   * math.Float32bits(float32(math.NaN()))+1
 			in: `go test fuzz v1
 float32(-0)
 float64(-0)
@@ -113,8 +119,8 @@ float32(NaN)
 float64(+Inf)
 float64(-Inf)
 float64(NaN)
-math.Float64frombits(9221120237041090560)
-math.Float32frombits(2143289343)`,
+math.Float64frombits(9221120237041090562)
+math.Float32frombits(2143289345)`,
 			ok: true,
 		},
 	}