diff --git a/src/core/operations/GenerateImage.mjs b/src/core/operations/GenerateImage.mjs
index 56b5798a..c276213d 100644
--- a/src/core/operations/GenerateImage.mjs
+++ b/src/core/operations/GenerateImage.mjs
@@ -74,12 +74,12 @@ class GenerateImage extends Operation {
             Bits: 1 / 8,
         };
 
-        const bytesPerPixel = bytePerPixelMap[mode];
-
-        if (bytesPerPixel === undefined) {
+        if (!Object.hasOwn(bytePerPixelMap, mode)) {
             throw new OperationError(`Unsupported Mode: (${mode})`);
         }
 
+        const bytesPerPixel = bytePerPixelMap[mode];
+
         if (bytesPerPixel > 0 && input.length % bytesPerPixel !== 0) {
             throw new OperationError(
                 `Number of bytes is not a divisor of ${bytesPerPixel}`,