--- a/h3/src/binding/indexing.c
+++ b/h3/src/binding/indexing.c
@@ -15,6 +15,7 @@
  */
 
 #include <postgres.h>
+#include <math.h>
 
 #if POSTGRESQL_VERSION_MAJOR >= 16
 #include "varatt.h" //VAR_SIZE and friends moved to here from postgres.h
