diff --git a/core/dive.c b/core/dive.c
index 414ad30f2..aac6cdc52 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -3151,7 +3151,7 @@ void split_divecomputer(const struct dive *src, int num, struct dive **out1, str
 fraction_t best_o2(depth_t depth, const struct dive *dive, bool in_planner)
 {
 	fraction_t fo2;
-	int po2 = in_planner ? prefs.bottompo2 : prefs.modpO2 * 1000;
+	int po2 = in_planner ? prefs.bottompo2 : (int)(prefs.modpO2 * 1000.0);
 
 	fo2.permille = (po2 * 100 / depth_to_mbar(depth.mm, dive)) * 10;	//use integer arithmetic to round down to nearest percent
 	// Don't permit >100% O2
diff --git a/qt-models/cylindermodel.cpp b/qt-models/cylindermodel.cpp
index 0824fe8eb..ae70e644b 100644
--- a/qt-models/cylindermodel.cpp
+++ b/qt-models/cylindermodel.cpp
@@ -230,7 +230,7 @@ QVariant CylindersModel::data(const QModelIndex &index, int role) const
 				return QStringLiteral("*");
 			} else {
 				pressure_t modpO2;
-				modpO2.mbar = inPlanner ? prefs.bottompo2 : prefs.modpO2 * 1000;
+				modpO2.mbar = inPlanner ? prefs.bottompo2 : (int)(prefs.modpO2 * 1000.0);
 				return get_depth_string(gas_mod(cyl->gasmix, modpO2, d, M_OR_FT(1,1)), true);
 			}
 		case MND: