diff --git a/native/android/app/src/main/java/app/comm/android/fbjni/PlatformSpecificTools.java b/native/android/app/src/main/java/app/comm/android/fbjni/PlatformSpecificTools.java
--- a/native/android/app/src/main/java/app/comm/android/fbjni/PlatformSpecificTools.java
+++ b/native/android/app/src/main/java/app/comm/android/fbjni/PlatformSpecificTools.java
@@ -60,9 +60,9 @@
 
     String filename;
     if (isAttachments) {
-      filename = String.join("_", "backup", backupID, "attachments");
+      filename = String.join("-", "backup", backupID, "attachments");
     } else {
-      filename = String.join("_", "backup", backupID);
+      filename = String.join("-", "backup", backupID);
     }
     return String.join(File.separator, backupDirPath, filename);
   }
diff --git a/native/ios/Comm/PlatformSpecificTools.mm b/native/ios/Comm/PlatformSpecificTools.mm
--- a/native/ios/Comm/PlatformSpecificTools.mm
+++ b/native/ios/Comm/PlatformSpecificTools.mm
@@ -83,9 +83,9 @@
   NSString *filename;
   if (isAttachments) {
     filename = [@[ @"backup", backupIDObjC, @"attachments" ]
-        componentsJoinedByString:@"_"];
+        componentsJoinedByString:@"-"];
   } else {
-    filename = [@[ @"backup", backupIDObjC ] componentsJoinedByString:@"_"];
+    filename = [@[ @"backup", backupIDObjC ] componentsJoinedByString:@"-"];
   }
   return [[backupDir URLByAppendingPathComponent:filename].path UTF8String];
 }