diff --git a/src/gsm/gsm0808_utils.c b/src/gsm/gsm0808_utils.c
index 00da04b..c636adf 100644
--- a/src/gsm/gsm0808_utils.c
+++ b/src/gsm/gsm0808_utils.c
@@ -104,7 +104,7 @@
 	OSMO_ASSERT(ss);
 	if (!elem)
 		return -EINVAL;
-	if (len <= 0)
+	if (len == 0)
 		return -EINVAL;
 
 	memset(ss, 0, sizeof(*ss));
@@ -261,7 +261,7 @@
 	OSMO_ASSERT(sc);
 	if (!elem)
 		return -EINVAL;
-	if (len <= 0)
+	if (len == 0)
 		return -EINVAL;
 
 	memset(sc, 0, sizeof(*sc));
@@ -377,7 +377,7 @@
 	OSMO_ASSERT(scl);
 	if (!elem)
 		return -EINVAL;
-	if (len <= 0)
+	if (len == 0)
 		return -EINVAL;
 
 	memset(scl, 0, sizeof(*scl));
@@ -461,7 +461,7 @@
 	OSMO_ASSERT(ct);
 	if (!elem)
 		return -EINVAL;
-	if (len <= 0)
+	if (len < 3 || len > 11)
 		return -EINVAL;
 
 	memset(ct, 0, sizeof(*ct));
@@ -537,7 +537,7 @@
 	OSMO_ASSERT(ei);
 	if (!elem)
 		return -EINVAL;
-	if (len <= 0)
+	if (len == 0)
 		return -EINVAL;
 
 	memset(ei, 0, sizeof(*ei));
@@ -614,7 +614,7 @@
 	OSMO_ASSERT(cil);
 	if (!elem)
 		return -EINVAL;
-	if (len <= 0)
+	if (len == 0)
 		return -EINVAL;
 
 	memset(cil, 0, sizeof(*cil));