diff --git a/types/index.d.ts b/types/index.d.ts
index 115d712..b585ca7 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -45,24 +45,28 @@ type DeepMergeObjectProps<
 	T2,
 	Options extends deepmerge.Options
 > = {} extends {
-	[K in keyof (T1 & T2)]: Options["customMerge"] extends undefined
-		? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
-		: ReturnType<NonNullable<Options["customMerge"]>>;
+	[K in keyof (T1 & T2)]: any;
 }
 	? {
 			[K in keyof T1]: Options["customMerge"] extends undefined
 				? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
-				: ReturnType<NonNullable<Options["customMerge"]>>;
+				: ReturnType<NonNullable<Options["customMerge"]>> extends undefined
+					? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
+					: ReturnType<NonNullable<ReturnType<NonNullable<Options["customMerge"]>>>>;
 	  } &
 			{
 				[K in keyof T2]: Options["customMerge"] extends undefined
 					? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
-					: ReturnType<NonNullable<Options["customMerge"]>>;
+					: ReturnType<NonNullable<Options["customMerge"]>> extends undefined
+						? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
+						: ReturnType<NonNullable<ReturnType<NonNullable<Options["customMerge"]>>>>;
 			}
 	: {
 			[K in keyof (T1 & T2)]: Options["customMerge"] extends undefined
 				? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
-				: ReturnType<NonNullable<Options["customMerge"]>>;
+				: ReturnType<NonNullable<Options["customMerge"]>> extends undefined
+					? DeepMerge<ValueOfKey<T1, K>, ValueOfKey<T2, K>, Options>
+					: ReturnType<NonNullable<ReturnType<NonNullable<Options["customMerge"]>>>>;
 	  };
 
 type DeepMergeArrays<