diff --git a/src/libsysprof/sysprof-proc-source.c b/src/libsysprof/sysprof-proc-source.c
index 7edaee01..9200b127 100644
--- a/src/libsysprof/sysprof-proc-source.c
+++ b/src/libsysprof/sysprof-proc-source.c
@@ -167,7 +167,7 @@ add_file (SysprofProcSource *self,
                                        -1,
                                        pid,
                                        path,
-                                       to_write > 0,
+                                       to_write == 0,
                                        (const guint8 *)data,
                                        this_write);
       data += this_write;