diff --git a/src/count_messages.cpp b/src/count_messages.cpp
index 8fa2970..ac01b79 100644
--- a/src/count_messages.cpp
+++ b/src/count_messages.cpp
@@ -2,6 +2,7 @@
 
 #ifdef __APPLE__
 #  define fseeko64 fseeko
+#  define ftello64 ftello
 #endif
 
 // counts messages in a file
diff --git a/src/filter_itch.cpp b/src/filter_itch.cpp
index 8817430..17a20f8 100644
--- a/src/filter_itch.cpp
+++ b/src/filter_itch.cpp
@@ -2,6 +2,7 @@
 
 #ifdef __APPLE__
 #  define fseeko64 fseeko
+#  define ftello64 ftello
 #endif
 
 // [[Rcpp::export]]
diff --git a/src/read_functions.cpp b/src/read_functions.cpp
index 9823b51..bdd8b59 100644
--- a/src/read_functions.cpp
+++ b/src/read_functions.cpp
@@ -2,6 +2,7 @@
 
 #ifdef __APPLE__
 #  define fseeko64 fseeko
+#  define ftello64 ftello
 #endif
 
 // [[Rcpp::export]]