diff --git a/src/sos_filter.c b/src/sos_filter.c
index 04eb366e..6e64bc0a 100644
--- a/src/sos_filter.c
+++ b/src/sos_filter.c
@@ -29,7 +29,7 @@ struct sos_filter {
     struct sos_filter_section filter[0];
 };
 
-inline uint8_t
+static inline uint8_t
 overflows_int32(int64_t value) {
     return value > (int64_t)INT32_MAX || value < (int64_t)INT32_MIN;
 }