diff --git a/src/vector.c b/src/vector.c
index 4b1171d..2e385ba 100644
--- a/src/vector.c
+++ b/src/vector.c
@@ -20,6 +20,7 @@
 #endif
 
 #if PG_VERSION_NUM < 130000
+#define TYPALIGN_DOUBLE 'd'
 #define TYPALIGN_INT 'i'
 #endif