diff --git a/acb.h b/acb.h
index 1ac3da68..54cbf12f 100644
--- a/acb.h
+++ b/acb.h
@@ -996,7 +996,7 @@ acb_printd(const acb_t z, slong digits)
     acb_fprintd(stdout, z, digits);
 }
 
-void acb_fprintn(FILE * fp, const acb_t z, long digits, ulong flags);
+void acb_fprintn(FILE * fp, const acb_t z, slong digits, ulong flags);
 
 ACB_INLINE void
 acb_printn(const acb_t x, slong digits, ulong flags)
diff --git a/acb/fprintn.c b/acb/fprintn.c
index 95d68168..c6618eaa 100644
--- a/acb/fprintn.c
+++ b/acb/fprintn.c
@@ -13,7 +13,7 @@
 #include "acb.h"
 
 void
-acb_fprintn(FILE * file, const acb_t z, long digits, ulong flags)
+acb_fprintn(FILE * file, const acb_t z, slong digits, ulong flags)
 {
     if (arb_is_zero(acb_imagref(z)))
     {