diff --git a/HISTORY.rst b/HISTORY.rst
index 17b53191..f165c8d6 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -17,6 +17,8 @@ PlatformIO 3.0
 ~~~~~~~~~~~~~~~~~~
 
 * Project Generator: fixed a VSCode C/C++'s "Cannot find" warning when CPPPATH folder does not exist
+* Fixed an "IndexError: list index out of range" for Arduino sketch preprocessor
+  (`issue #2268 <https://github.com/platformio/platformio-core/issues/2268>`_)
 
 3.6.6 (2019-03-29)
 ~~~~~~~~~~~~~~~~~~
diff --git a/platformio/builder/tools/piomisc.py b/platformio/builder/tools/piomisc.py
index e6f846e0..1118ac35 100644
--- a/platformio/builder/tools/piomisc.py
+++ b/platformio/builder/tools/piomisc.py
@@ -157,9 +157,7 @@ class InoToCPPConverter(object):
         return total
 
     def append_prototypes(self, contents):
-        prototypes = self._parse_prototypes(contents)
-        if not prototypes:
-            return contents
+        prototypes = self._parse_prototypes(contents) or []
 
         # skip already declared prototypes
         declared = set(
@@ -168,6 +166,9 @@ class InoToCPPConverter(object):
             m for m in prototypes if m.group(1).strip() not in declared
         ]
 
+        if not prototypes:
+            return contents
+
         prototype_names = set(m.group(3).strip() for m in prototypes)
         split_pos = prototypes[0].start()
         match_ptrs = re.search(