diff --git a/planarity/c/graphLib/io/graphIO.c b/planarity/c/graphLib/io/graphIO.c
index 41cba4c..e697257 100644
--- a/planarity/c/graphLib/io/graphIO.c
+++ b/planarity/c/graphLib/io/graphIO.c
@@ -351,7 +351,7 @@ int _ReadLEDAGraph(graphP theGraph, strOrFileP inputContainer)
 
     int graphType = 0;
     int N = 0, M = 0, u = NIL, v = NIL;
-    int zeroBasedOffset = gp_LowerBoundVertexStorage(theGraph) == 0 ? 1 : 0;
+    int zeroBasedOffset = (gp_LowerBoundVertexStorage(theGraph) == 0) ? 1 : 0;
     char Line[MAXLINE + 1];
 
     memset(Line, '\0', (MAXLINE + 1));