5 files changed, 17 insertions, 6 deletions
diff --git a/core/dive.c b/core/dive.c
index 53ca49bfd..a8814413a 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -2205,8 +2205,15 @@ void cylinder_renumber(struct dive *dive, int mapping[])
 		dc_cylinder_renumber(dive, dc, mapping);
 }
 
+static bool gasmix_is_invalid(struct gasmix mix)
+{
+	return mix.o2.permille < 0;
+}
+
 int same_gasmix(struct gasmix a, struct gasmix b)
 {
+	if (gasmix_is_invalid(a) || gasmix_is_invalid(b))
+		return 0;
 	if (gasmix_is_air(a) && gasmix_is_air(b))
 		return 1;
 	return a.o2.permille == b.o2.permille && a.he.permille == b.he.permille;
@@ -4314,6 +4321,6 @@ struct gasmix get_gasmix(const struct dive *dive, const struct divecomputer *dc,
 struct gasmix get_gasmix_at_time(const struct dive *d, const struct divecomputer *dc, duration_t time)
 {
 	const struct event *ev = NULL;
-	struct gasmix gasmix = { 0 };
+	struct gasmix gasmix = gasmix_air;
 	return get_gasmix(d, dc, time.seconds, &ev, gasmix);
 }
diff --git a/core/dive.h b/core/dive.h
index 0cc3150ce..8b8b9fbf0 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -34,10 +34,14 @@ extern const char *cylinderuse_text[];
 extern const char *divemode_text_ui[];
 extern const char *divemode_text[];
 
+// o2 == 0 && he == 0 -> air
+// o2 < 0 -> invalid
 struct gasmix {
 	fraction_t o2;
 	fraction_t he;
 };
+static const struct gasmix gasmix_invalid = { { -1 }, { -1 } };
+static const struct gasmix gasmix_air = { { 0 }, { 0 } };
 
 typedef struct
 {
diff --git a/core/divelist.c b/core/divelist.c
index f643d14f6..1906d002a 100644
--- a/core/divelist.c
+++ b/core/divelist.c
@@ -405,7 +405,7 @@ static int calculate_sac(const struct dive *dive)
 static void add_dive_to_deco(struct deco_state *ds, struct dive *dive)
 {
 	struct divecomputer *dc = &dive->dc;
-	struct gasmix gasmix = { 0 };
+	struct gasmix gasmix = gasmix_air;
 	int i;
 	const struct event *ev = NULL, *evd = NULL;
 	enum divemode_t current_divemode = UNDEF_COMP_TYPE;
diff --git a/core/plannernotes.c b/core/plannernotes.c
index 133f9a591..f768698ac 100644
--- a/core/plannernotes.c
+++ b/core/plannernotes.c
@@ -76,7 +76,7 @@ void add_plan_to_notes(struct diveplan *diveplan, struct dive *dive, bool show_d
 	struct membuffer icdbuf = { 0 };
 	const char *deco, *segmentsymbol;
 	int lastdepth = 0, lasttime = 0, lastsetpoint = -1, newdepth = 0, lastprintdepth = 0, lastprintsetpoint = -1;
-	struct gasmix lastprintgasmix = {{ -1 }, { -1 }};
+	struct gasmix lastprintgasmix = gasmix_invalid;
 	struct divedatapoint *dp = diveplan->dp;
 	bool plan_verbatim = prefs.verbatim_plan;
 	bool plan_display_runtime = prefs.display_runtime;
diff --git a/core/profile.c b/core/profile.c
index 47fc97723..af7ebe271 100644
--- a/core/profile.c
+++ b/core/profile.c
@@ -780,7 +780,7 @@ static unsigned int matching_gases(struct dive *dive, struct gasmix gasmix)
 
 static void calculate_sac(struct dive *dive, struct divecomputer *dc, struct plot_info *pi)
 {
-	struct gasmix gasmix = { 0 };
+	struct gasmix gasmix = gasmix_invalid;
 	const struct event *ev = NULL;
 	unsigned int gases = 0;
 
@@ -1021,7 +1021,7 @@ void calculate_deco_information(struct deco_state *ds, const struct deco_state *
 		int last_ndl_tts_calc_time = 0, first_ceiling = 0, current_ceiling, last_ceiling = 0, final_tts = 0 , time_clear_ceiling = 0;
 		if (decoMode() == VPMB)
 			ds->first_ceiling_pressure.mbar = depth_to_mbar(first_ceiling, dive);
-		struct gasmix gasmix = { 0 };
+		struct gasmix gasmix = gasmix_invalid;
 		const struct event *ev = NULL, *evd = NULL;
 		enum divemode_t current_divemode = UNDEF_COMP_TYPE;
 
@@ -1210,7 +1210,7 @@ static void calculate_gas_information_new(struct dive *dive, struct divecomputer
 {
 	int i;
 	double amb_pressure;
-	struct gasmix gasmix = { 0 };
+	struct gasmix gasmix = gasmix_invalid;
 	const struct event *evg = NULL, *evd = NULL;
 	enum divemode_t current_divemode = UNDEF_COMP_TYPE;