diff --git a/src/libsysprof/sysprof-battery-source.c b/src/libsysprof/sysprof-battery-source.c
index 0b12a6e7..92db4822 100644
--- a/src/libsysprof/sysprof-battery-source.c
+++ b/src/libsysprof/sysprof-battery-source.c
@@ -237,10 +237,9 @@ sysprof_battery_source_start (SysprofSource *source)
 {
   SysprofBatterySource *self = (SysprofBatterySource *)source;
 
-  self->poll_source = g_timeout_add_seconds (1, sysprof_battery_source_poll_cb, self);
-
   g_assert (SYSPROF_IS_BATTERY_SOURCE (self));
 
+  self->poll_source = g_timeout_add_seconds (1, sysprof_battery_source_poll_cb, self);
 }
 
 static void