diff --git a/lib/xmet/sounding.py b/lib/xmet/sounding.py
index ce63863..00de8b7 100644
--- a/lib/xmet/sounding.py
+++ b/lib/xmet/sounding.py
@@ -10,6 +10,7 @@ from xmet.series import Series, SeriesIntersection
 from xmet.thermo import follow_dry_adiabat, \
                         follow_moist_adiabat, \
                         follow_saturated_mixing_ratio, \
+                        pressure_height, \
                         kelvin
 
 LAPSE_RATE_DRY   = 9.8 # degrees C per 1000m