diff --git a/.changeset/modern-mugs-raise.md b/.changeset/modern-mugs-raise.md
new file mode 100644
index 0000000000..0796acf9f8
--- /dev/null
+++ b/.changeset/modern-mugs-raise.md
@@ -0,0 +1,5 @@
+---
+"astro": patch
+---
+
+Fixes Picture component specialFormatsFallback fallback check
diff --git a/packages/astro/components/Picture.astro b/packages/astro/components/Picture.astro
index f23ab6ccce..6dcc50c8e1 100644
--- a/packages/astro/components/Picture.astro
+++ b/packages/astro/components/Picture.astro
@@ -45,7 +45,7 @@ let resultFallbackFormat = fallbackFormat ?? defaultFallbackFormat;
 if (
 	!fallbackFormat &&
 	isESMImportedImage(originalSrc) &&
-	originalSrc.format in specialFormatsFallback
+	(specialFormatsFallback as ReadonlyArray<string>).includes(originalSrc.format)
 ) {
 	resultFallbackFormat = originalSrc.format;
 }