diff --git a/pcbnew/dialogs/dialog_board_reannotate.cpp b/pcbnew/dialogs/dialog_board_reannotate.cpp
index d3a2dbe1ba..789eb2c08f 100644
--- a/pcbnew/dialogs/dialog_board_reannotate.cpp
+++ b/pcbnew/dialogs/dialog_board_reannotate.cpp
@@ -190,7 +190,7 @@ REFDES_PREFIX_INFO* DIALOG_BOARD_REANNOTATE::GetOrBuildRefDesInfo( const wxStrin
     // Wasn't in the info array so add it
     REFDES_PREFIX_INFO newtype;
     newtype.RefDesPrefix = aRefDesPrefix;
-    newtype.LastUsedRefDes = aStartRefDes - 1;
+    newtype.LastUsedRefDes = std::max( aStartRefDes - 1, 0 );
     m_refDesPrefixInfos.push_back( newtype );
 
     return &m_refDesPrefixInfos.back();