diff --git a/build_tools/format-diff.sh b/build_tools/format-diff.sh
index af15859cf..c2842dfa4 100755
--- a/build_tools/format-diff.sh
+++ b/build_tools/format-diff.sh
@@ -136,9 +136,11 @@ then
   FORMAT_UPSTREAM_MERGE_BASE="$(git merge-base "$FORMAT_UPSTREAM" HEAD)"
   # Get the differences
   diffs=$(git diff -U0 "$FORMAT_UPSTREAM_MERGE_BASE" | $CLANG_FORMAT_DIFF -p 1)
+  echo "Checking format of changes not yet in $FORMAT_UPSTREAM..."
 else
   # Check the format of uncommitted lines,
   diffs=$(git diff -U0 HEAD | $CLANG_FORMAT_DIFF -p 1)
+  echo "Checking format of uncommitted changes..."
 fi
 
 if [ -z "$diffs" ]
diff --git a/env/fs_readonly.h b/env/fs_readonly.h
index 77ea1ded8..89875106e 100644
--- a/env/fs_readonly.h
+++ b/env/fs_readonly.h
@@ -23,7 +23,7 @@ class ReadOnlyFileSystem : public FileSystemWrapper {
   }
 
  public:
-  ReadOnlyFileSystem(const std::shared_ptr<FileSystem>& base)
+  explicit ReadOnlyFileSystem(const std::shared_ptr<FileSystem>& base)
       : FileSystemWrapper(base) {}
 
   IOStatus NewWritableFile(const std::string& /*fname*/,
@@ -61,10 +61,17 @@ class ReadOnlyFileSystem : public FileSystemWrapper {
                      IODebugContext* /*dbg*/) override {
     return FailReadOnly();
   }
-  IOStatus CreateDirIfMissing(const std::string& /*dirname*/,
-                              const IOOptions& /*options*/,
-                              IODebugContext* /*dbg*/) override {
-    return FailReadOnly();
+  IOStatus CreateDirIfMissing(const std::string& dirname,
+                              const IOOptions& options,
+                              IODebugContext* dbg) override {
+    // Allow if dir already exists
+    bool is_dir = false;
+    IOStatus s = IsDirectory(dirname, options, &is_dir, dbg);
+    if (s.ok() && is_dir) {
+      return s;
+    } else {
+      return FailReadOnly();
+    }
   }
   IOStatus DeleteDir(const std::string& /*dirname*/,
                      const IOOptions& /*options*/,
diff --git a/env/fs_remap.h b/env/fs_remap.h
index f95ff9de2..4975822f6 100644
--- a/env/fs_remap.h
+++ b/env/fs_remap.h
@@ -20,7 +20,7 @@ namespace ROCKSDB_NAMESPACE {
 // guarantees.
 class RemapFileSystem : public FileSystemWrapper {
  public:
-  RemapFileSystem(const std::shared_ptr<FileSystem>& base);
+  explicit RemapFileSystem(const std::shared_ptr<FileSystem>& base);
 
  protected:
   // Returns status and mapped-to path in the wrapped filesystem.
diff --git a/utilities/backupable/backupable_db_test.cc b/utilities/backupable/backupable_db_test.cc
index f4e7f3d09..7d24936f5 100644
--- a/utilities/backupable/backupable_db_test.cc
+++ b/utilities/backupable/backupable_db_test.cc
@@ -2660,6 +2660,7 @@ TEST_F(BackupableDBTest, OpenBackupAsReadOnlyDB) {
   backup_engine_->GetBackupInfo(&backup_info, /*with file details*/ true);
   ASSERT_EQ(backup_info.size(), 2);
   CloseBackupEngine();
+  opts.create_if_missing = true;  // check also OK (though pointless)
   opts.env = backup_info[1].env_for_open.get();
   name = backup_info[1].name_for_open;
   // Note: keeping backup_info[1] alive