diff --git a/src/rinterface_extra.c b/src/rinterface_extra.c
index 06795f2fd0..68f3be67e7 100644
--- a/src/rinterface_extra.c
+++ b/src/rinterface_extra.c
@@ -28,6 +28,7 @@
 #include <R_ext/Altrep.h>
 
 #include <stdio.h>
+#include <inttypes.h>
 
 #if defined(__SANITIZE_ADDRESS__)
 #  define IGRAPH_SANITIZER_AVAILABLE 1
@@ -73,8 +74,8 @@ enum igraph_versions {
 void R_check_int_scalar(SEXP value)
 {
   if (Rf_xlength(value) != 1) {
-    igraph_errorf("Expecting a scalar integer but received a vector of length %lu.",
-                    __FILE__, __LINE__, IGRAPH_EINVAL, (unsigned long) Rf_xlength(value));
+    igraph_errorf("Expecting a scalar integer but received a vector of length %" PRIuPTR ".",
+                    __FILE__, __LINE__, IGRAPH_EINVAL, (uintptr_t) Rf_xlength(value));
   }
   if (((igraph_integer_t) REAL(value)[0]) != REAL(value)[0]) {
     igraph_errorf("The value %.17g is not representable as an integer.",
@@ -85,16 +86,16 @@ void R_check_int_scalar(SEXP value)
 void R_check_real_scalar(SEXP value)
 {
   if (Rf_xlength(value) != 1) {
-    igraph_errorf("Expecting a scalar real but received a vector of length %lu.",
-                    __FILE__, __LINE__, IGRAPH_EINVAL, (unsigned long) Rf_xlength(value));
+    igraph_errorf("Expecting a scalar real but received a vector of length %" PRIuPTR ".",
+                    __FILE__, __LINE__, IGRAPH_EINVAL, (uintptr_t) Rf_xlength(value));
   }
 }
 
 void R_check_bool_scalar(SEXP value)
 {
   if (Rf_xlength(value) != 1) {
-    igraph_errorf("Expecting a scalar logical but received a vector of length %lu.",
-                    __FILE__, __LINE__, IGRAPH_EINVAL, (unsigned long) Rf_xlength(value));
+    igraph_errorf("Expecting a scalar logical but received a vector of length %" PRIuPTR ".",
+                    __FILE__, __LINE__, IGRAPH_EINVAL, (uintptr_t) Rf_xlength(value));
   }
 }