diff --git a/src/gui/editors/PianoRoll.cpp b/src/gui/editors/PianoRoll.cpp
index a1fcdc6d8..36505e982 100644
--- a/src/gui/editors/PianoRoll.cpp
+++ b/src/gui/editors/PianoRoll.cpp
@@ -550,7 +550,10 @@ void PianoRoll::markSemiTone( int i )
 				for (int ix = 0; ix < aok.size(); ++ix)
 				{
 					i = std::find(m_markedSemiTones.begin(), m_markedSemiTones.end(), aok.at(ix));
-					m_markedSemiTones.erase(i);
+					if (i != m_markedSemiTones.end())
+					{
+						m_markedSemiTones.erase(i);
+					}
 				}
 			}
 			else