diff --git a/h5_merger.py b/h5_merger.py
index 0303f778..a9e0877e 100644
--- a/h5_merger.py
+++ b/h5_merger.py
@@ -371,7 +371,7 @@ def __init__(self, h5_out, h5_tables=None, ms_files=None, h5_time_freq=None, con
             self.ax_time = array([])
             self.ax_freq = array([])
             for m in self.ms:
-                t = ct.taql('SELECT CHAN_FREQ, CHAN_WIDTH FROM ' + m + '::SPECTRAL_WINDOW')
+                t = ct.taql('SELECT CHAN_FREQ, CHAN_WIDTH FROM ' + os.path.abspath(m) + '::SPECTRAL_WINDOW')
                 self.ax_freq = append(self.ax_freq, t.getcol('CHAN_FREQ')[0])
                 t.close()