diff --git a/src/transform/plugins/images/index.ts b/src/transform/plugins/images/index.ts
index 0d976dbd..e0d23a04 100644
--- a/src/transform/plugins/images/index.ts
+++ b/src/transform/plugins/images/index.ts
@@ -63,7 +63,7 @@ function convertSvg(
     try {
         let content: string;
         if (envApi) {
-            content = envApi?.readFile(relative(root, path), 'utf8');
+            content = envApi?.readFile(relative(root, path), 'utf8') as string;
         } else {
             content = readFileSync(path, 'utf8');
         }
diff --git a/src/transform/utilsFS.ts b/src/transform/utilsFS.ts
index 5078e209..70738d5f 100644
--- a/src/transform/utilsFS.ts
+++ b/src/transform/utilsFS.ts
@@ -61,7 +61,7 @@ export function getFileTokens(path: string, state: StateCore, options: GetFileTo
     }
 
     if (envApi) {
-        content = envApi.readFile(relative(envApi.root, path), 'utf-8');
+        content = envApi.readFile(relative(envApi.root, path), 'utf-8') as string;
     } else if (filesCache[path]) {
         content = filesCache[path];
     } else {
diff --git a/src/transform/yfmlint/index.ts b/src/transform/yfmlint/index.ts
index 14eee4cd..97a00838 100644
--- a/src/transform/yfmlint/index.ts
+++ b/src/transform/yfmlint/index.ts
@@ -111,9 +111,9 @@ namespace yfmlint {
         distRoot: string;
         copyFile: (from: string, to: string) => void;
         copyFileAsync: (from: string, to: string) => void;
-        writeFile: (to: string, data: string) => void;
-        writeFileAsync: (to: string, data: string) => void;
-        readFile: (path: string, encoding: BufferEncoding) => string;
+        writeFile: (to: string, data: string | Uint8Array) => void;
+        writeFileAsync: (to: string, data: string | Uint8Array) => void;
+        readFile: (path: string, encoding: BufferEncoding) => string | Uint8Array;
         fileExists: (path: string) => boolean;
         getFileVars: (path: string) => Record<string, string>;
     }