diff --git a/src/tests/common-files/gnuplot_i.h b/src/tests/common-files/gnuplot_i.h
index 6bb6d7d4f..549230c4a 100644
--- a/src/tests/common-files/gnuplot_i.h
+++ b/src/tests/common-files/gnuplot_i.h
@@ -1967,7 +1967,7 @@ bool Gnuplot::get_program_path()
     size_t len = strlen(path);
     if (path && len < 4046 * sizeof(char))
         {
-            strncpy(secured_path, path, len);
+            strncpy(secured_path, path, len - 1);
         }
     else
         {