diff --git a/lang/c/src/schema.c b/lang/c/src/schema.c
index a4d8e9f898a..9e91aca8da1 100644
--- a/lang/c/src/schema.c
+++ b/lang/c/src/schema.c
@@ -325,6 +325,11 @@ avro_schema_t avro_schema_fixed_ns(const char *name, const char *space,
 		return NULL;
 	}
 
+	if (size < 0) {
+		avro_set_error("Invalid size for fixed schema");
+		return NULL;
+	}
+
 	struct avro_fixed_schema_t *fixed =
 	    (struct avro_fixed_schema_t *) avro_new(struct avro_fixed_schema_t);
 	if (!fixed) {
diff --git a/lang/c/tests/schema_tests/fail/fixed_negative_size b/lang/c/tests/schema_tests/fail/fixed_negative_size
new file mode 100644
index 00000000000..6ff5cf8eca4
--- /dev/null
+++ b/lang/c/tests/schema_tests/fail/fixed_negative_size
@@ -0,0 +1,3 @@
+{"type": "fixed",
+ "name": "F",
+ "size": -1}