diff --git a/src/dfmt/formatter.d b/src/dfmt/formatter.d
index 5456f7f..e78a132 100644
--- a/src/dfmt/formatter.d
+++ b/src/dfmt/formatter.d
@@ -557,6 +557,10 @@ private:
         writeToken();
         if (p == tok!"(")
         {
+            // If the file starts with an open paren, just give up. This isn't
+            // valid D code.
+            if (index < 2)
+                return;
             if (isBlockHeaderToken(tokens[index - 2].type))
                 indents.push(tok!")");
             else
@@ -564,6 +568,9 @@ private:
             spaceAfterParens = true;
             parenDepth++;
         }
+        // No heuristics apply if we can't look before the opening paren/bracket
+        if (index < 1)
+            return;
         immutable bool arrayInitializerStart = p == tok!"[" && linebreakHints.length != 0
             && astInformation.arrayStartLocations.canFindIndex(tokens[index - 1].index);
         if (arrayInitializerStart)