diff --git a/shiny/iconvg/decode_test.go b/shiny/iconvg/decode_test.go
index fae6ca7..c1778e6 100644
--- a/shiny/iconvg/decode_test.go
+++ b/shiny/iconvg/decode_test.go
@@ -155,7 +155,7 @@
 			continue
 		}
 		wantFilename := filepath.FromSlash(tc.filename) + ".ivg.disassembly"
-		if overwriteTestdataFiles {
+		if *updateFlag {
 			if err := ioutil.WriteFile(filepath.FromSlash(wantFilename), got, 0666); err != nil {
 				t.Errorf("%s: WriteFile: %v", tc.filename, err)
 			}
@@ -173,7 +173,7 @@
 	}
 }
 
-func TestRasterizer(t *testing.T) {
+func TestDecodeAndRasterize(t *testing.T) {
 	for _, tc := range testdataTestCases {
 		ivgData, err := ioutil.ReadFile(filepath.FromSlash(tc.filename) + ".ivg")
 		if err != nil {
@@ -218,7 +218,7 @@
 				wantFilename += "." + variant
 			}
 			wantFilename += ".png"
-			if overwriteTestdataFiles {
+			if *updateFlag {
 				if err := encodePNG(filepath.FromSlash(wantFilename), got); err != nil {
 					t.Errorf("%s %q variant: encodePNG: %v", tc.filename, variant, err)
 				}
diff --git a/shiny/iconvg/doc.go b/shiny/iconvg/doc.go
index bfa7310..8627814 100644
--- a/shiny/iconvg/doc.go
+++ b/shiny/iconvg/doc.go
@@ -28,6 +28,9 @@
 Nonetheless, at typical scales, e.g. up to 4096 × 4096, such differences are
 not expected to be perceptible to the naked eye.
 
+The encoder aims to emit byte-identical output for the same input, independent
+of the platform (and specifically its floating-point hardware).
+
 
 Structure
 
@@ -474,7 +477,7 @@
 
 The production version of the "action/info" icon from the Material Design icon
 set is defined by the following SVG, also available at
-https://github.com/google/material-design-icons/blob/master/action/svg/production/ic_info_48px.svg:
+https://github.com/google/material-design-icons/blob/3.0.2/action/svg/production/ic_info_48px.svg:
 
 	<svg xmlns="http://www.w3.org/2000/svg" width="48" height="48" viewBox="0 0 48 48">
 	<path d="M24 4C12.95 4 4 12.95 4 24s8.95 20 20 20 20-8.95 20-20S35.05 4 24 4z
diff --git a/shiny/iconvg/encode.go b/shiny/iconvg/encode.go
index c9c3ac9..6c27f83 100644
--- a/shiny/iconvg/encode.go
+++ b/shiny/iconvg/encode.go
@@ -34,6 +34,9 @@
 // The zero value is usable. Calling Reset, which is optional, sets the
 // Metadata for the subsequent encoded form. If Reset is not called before
 // other Encoder methods, the default metadata is implied.
+//
+// It aims to emit byte-identical Bytes output for the same input, independent
+// of the platform (and specifically its floating-point hardware).
 type Encoder struct {
 	// HighResolutionCoordinates is whether the encoder should encode
 	// coordinate numbers for subsequent paths at the best possible resolution
@@ -410,16 +413,21 @@
 // axis vectors (rx, ry) and (sx, sy) such that (cx+rx, cy+ry) and (cx+sx,
 // cy+sy) are on the ellipse.
 func (e *Encoder) SetEllipticalGradient(cBase, nBase uint8, cx, cy, rx, ry, sx, sy float32, spread GradientSpread, stops []GradientStop) {
+	// Explicitly disable FMA in the floating-point calculations below
+	// to get consistent results on all platforms, and in turn produce
+	// a byte-identical encoding.
+	// See https://golang.org/ref/spec#Floating_point_operators and issue 43219.
+
 	// See the package documentation's appendix for a derivation of the
 	// transformation matrix.
-	invRSSR := 1 / (rx*sy - sx*ry)
+	invRSSR := 1 / (float32(rx*sy) - float32(sx*ry))
 
 	ma := +sy * invRSSR
 	mb := -sx * invRSSR
-	mc := -ma*cx - mb*cy
+	mc := -float32(ma*cx) - float32(mb*cy)
 	md := -ry * invRSSR
 	me := +rx * invRSSR
-	mf := -md*cx - me*cy
+	mf := -float32(md*cx) - float32(me*cy)
 
 	e.SetGradient(cBase, nBase, true, f32.Aff3{
 		ma, mb, mc,
diff --git a/shiny/iconvg/encode_test.go b/shiny/iconvg/encode_test.go
index 8091447..8c2592c 100644
--- a/shiny/iconvg/encode_test.go
+++ b/shiny/iconvg/encode_test.go
@@ -6,35 +6,28 @@
 
 import (
 	"bytes"
+	"flag"
 	"image/color"
 	"io/ioutil"
 	"math"
 	"path/filepath"
+	"runtime"
 	"strconv"
 	"testing"
 
 	"golang.org/x/image/math/f32"
 )
 
-// overwriteTestdataFiles is temporarily set to true when adding new
-// testdataTestCases.
-const overwriteTestdataFiles = false
-
-// TestOverwriteTestdataFilesIsFalse tests that any change to
-// overwriteTestdataFiles is only temporary. Programmers are assumed to run "go
-// test" before sending out for code review or committing code.
-func TestOverwriteTestdataFilesIsFalse(t *testing.T) {
-	if overwriteTestdataFiles {
-		t.Errorf("overwriteTestdataFiles is true; do not commit code changes")
-	}
-}
+// updateFlag controls whether to overwrite testdata files during tests.
+// This can be useful when adding new testdataTestCases.
+var updateFlag = flag.Bool("update", false, "Overwrite testdata files.")
 
 func testEncode(t *testing.T, e *Encoder, wantFilename string) {
 	got, err := e.Bytes()
 	if err != nil {
 		t.Fatalf("encoding: %v", err)
 	}
-	if overwriteTestdataFiles {
+	if *updateFlag {
 		if err := ioutil.WriteFile(filepath.FromSlash(wantFilename), got, 0666); err != nil {
 			t.Fatalf("WriteFile: %v", err)
 		}
@@ -45,7 +38,16 @@
 		t.Fatalf("ReadFile: %v", err)
 	}
 	if !bytes.Equal(got, want) {
-		t.Fatalf("\ngot  %d bytes:\n% x\nwant %d bytes:\n% x", len(got), got, len(want), want)
+		// The IconVG encoder is expected to be completely deterministic across all
+		// platforms and Go compilers, so check that we get exactly the right bytes.
+		//
+		// If we get slightly different bytes on some supported platform (for example,
+		// a new GOOS/GOARCH port, or a different but spec-compliant Go compiler) due
+		// to non-determinism in floating-point math, the encoder needs to be fixed.
+		//
+		// See golang.org/issue/43219#issuecomment-748531069.
+		t.Fatalf("\ngot  %d bytes (on GOOS=%s GOARCH=%s, using compiler %q):\n% x\nwant %d bytes:\n% x",
+			len(got), runtime.GOOS, runtime.GOARCH, runtime.Compiler, got, len(want), want)
 	}
 }
 
@@ -144,7 +146,7 @@
 
 	stops []GradientStop
 }{{
-// The 0th element is unused.
+	// The 0th element is unused.
 }, {
 	radial: true,
 	cx:     -102.14,
diff --git a/shiny/iconvg/testdata/README b/shiny/iconvg/testdata/README
index 22b9579..ce53d8c 100644
--- a/shiny/iconvg/testdata/README
+++ b/shiny/iconvg/testdata/README
@@ -1,6 +1,6 @@
 action-info.svg comes from the Material Design icon set. See
 action/svg/production/ic_info_48px.svg in the
-github.com/google/material-design-icons repository.
+github.com/google/material-design-icons repository at the tag 3.0.2.
 
 action-info.{lo,hi}res.ivg are low- and high-resolution IconVG versions of that
 SVG file. Low resolution means that coordinates are quantized to 1/64th of a