diff --git a/internal/warpc/avif_integration_test.go b/internal/warpc/avif_integration_test.go
index 7c0b3e0fa..9b3b68cb3 100644
--- a/internal/warpc/avif_integration_test.go
+++ b/internal/warpc/avif_integration_test.go
@@ -82,9 +82,11 @@ text:{{ ($img.Process "avif text").RelPermalink }}|
 
 	b := hugolib.Test(t, files)
 	b.AssertFileContent("public/index.html",
-		"default:/logo_hu_add3d7dfc55b7f80.avif|",
-		"photo:/logo_hu_add3d7dfc55b7f80.avif|",
-		"text:/logo_hu_b7080fe2a2e2a664.avif|")
+		`
+default:/logo_hu_72e150ce03376cfd.avif|
+photo:/logo_hu_72e150ce03376cfd.avif|
+text:/logo_hu_9de8f282912bc925.avif|
+`)
 }
 
 // See issue 14985.
diff --git a/resources/images/config.go b/resources/images/config.go
index ccc5e360d..93454c222 100644
--- a/resources/images/config.go
+++ b/resources/images/config.go
@@ -84,6 +84,13 @@ var (
 	// Increment to mark all processed images as stale. Only use when absolutely needed.
 	// See the finer grained smartCropVersionNumber.
 	mainImageVersionNumber = 1
+
+	// Increment a format's version number to mark all processed images targeting
+	// that format as stale, e.g. after a change to its encoder. This is finer
+	// grained than mainImageVersionNumber, which invalidates every format.
+	formatVersionNumbers = map[Format]int{
+		AVIF: 1,
+	}
 )
 
 var anchorPositions = map[string]gift.Anchor{
@@ -391,6 +398,10 @@ func DecodeImageConfig(options []string, defaults *config.ConfigNamespace[Imagin
 		options = append(options, strconv.Itoa(mainImageVersionNumber))
 	}
 
+	if v := formatVersionNumbers[c.TargetFormat]; v > 0 {
+		options = append(options, "tfv"+strconv.Itoa(v))
+	}
+
 	usesSmartCrop := c.Anchor == SmartCropAnchor && (c.Action == ActionCrop || c.Action == ActionFill)
 	if smartCropVersionNumber > 0 && usesSmartCrop {
 		options = append(options, strconv.Itoa(smartCropVersionNumber))
diff --git a/resources/images/config_test.go b/resources/images/config_test.go
index 9206c041d..ad6cfbd00 100644
--- a/resources/images/config_test.go
+++ b/resources/images/config_test.go
@@ -229,6 +229,30 @@ func TestImageConfigAvifDefaultQuality(t *testing.T) {
 	c.Assert(quality(cfg, "avif", "q33"), qt.Equals, 33)
 }
 
+// See issue 14990.
+func TestImageConfigFormatVersionNumber(t *testing.T) {
+	c := qt.New(t)
+
+	cfg, err := DecodeConfig(map[string]any{})
+	c.Assert(err, qt.IsNil)
+
+	key := func(f string) string {
+		conf, err := DecodeImageConfig([]string{"resize", "100x", f}, cfg, JPEG)
+		c.Assert(err, qt.IsNil)
+		return conf.Key
+	}
+
+	avifBefore, jpgBefore := key("avif"), key("jpg")
+
+	orig := formatVersionNumbers[AVIF]
+	defer func() { formatVersionNumbers[AVIF] = orig }()
+	formatVersionNumbers[AVIF] = orig + 1
+
+	// Bumping the AVIF version invalidates AVIF images only.
+	c.Assert(key("avif"), qt.Not(qt.Equals), avifBefore)
+	c.Assert(key("jpg"), qt.Equals, jpgBefore)
+}
+
 func TestDecodeImageConfig(t *testing.T) {
 	for i, this := range []struct {
 		action string