diff --git a/integration/simple-long/simple.ts b/integration/simple-long/simple.ts
index 95c7eda7a..87561d012 100644
--- a/integration/simple-long/simple.ts
+++ b/integration/simple-long/simple.ts
@@ -227,7 +227,7 @@ export const SimpleWithMap = {
     );
     message.longLookup = Object.entries(object.longLookup ?? {}).reduce<{ [key: string]: Long }>(
       (acc, [key, value]) => {
-        acc[key] = Long.fromString(value as string);
+        acc[key] = Long.fromValue(value as Long | string);
         return acc;
       },
       {}
diff --git a/src/main.ts b/src/main.ts
index 5cf94537c..8b7ddb02c 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -990,7 +990,7 @@ function generateFromJson(ctx: Context, fullName: string, messageDesc: Descripto
                 return code`${utils.bytesFromBase64}(${from} as string)`;
               }
             } else if (isLong(valueType) && options.forceLong === LongOption.LONG) {
-              return code`Long.fromString(${from} as string)`;
+              return code`Long.fromValue(${from} as Long | string)`;
             } else if (isEnum(valueType)) {
               return code`${from} as number`;
             } else {