diff --git a/bin/git-linguist b/bin/git-linguist
index 8f4ce0155a..5353dc0e1b 100755
--- a/bin/git-linguist
+++ b/bin/git-linguist
@@ -112,7 +112,7 @@ def git_linguist(args)
 
     opts.on("-f", "--force", "Force a full rescan") { incremental = false }
     opts.on("-c", "--commit=COMMIT", "Commit to index") { |v| commit = v}
-    opts.on("-t", "--tree-size=NUMBER", "Maximum number of files scanned to detect languages (default: 100,000)" ) { |t| tree_size = t }
+    opts.on("-t", "--tree-size=NUMBER", Integer, "Maximum number of files scanned to detect languages (default: 100,000)" ) { |t| tree_size = t }
   end
 
   parser.parse!(args)
diff --git a/bin/github-linguist b/bin/github-linguist
index 959110836b..abe4a056cb 100755
--- a/bin/github-linguist
+++ b/bin/github-linguist
@@ -33,7 +33,7 @@ def github_linguist(args)
     opts.on("-r", "--rev REV", String,
             "Analyze specific git revision",
             "defaults to HEAD, see gitrevisions(1) for alternatives") { |r| rev = r }
-    opts.on("-t", "--tree-size=NUMBER", "Maximum number of files scanned to detect languages (default: 100,000)") { |t| tree_size = t }
+    opts.on("-t", "--tree-size=NUMBER", Integer, "Maximum number of files scanned to detect languages (default: 100,000)") { |t| tree_size = t }
     opts.on("-h", "--help", "Display a short usage summary, then exit") do
       puts opts
       exit