diff --git a/src/os/aix/perfstat/sigar_perfstat.c b/src/os/aix/perfstat/sigar_perfstat.c
index 71c5ae2a..78e55a9d 100644
--- a/src/os/aix/perfstat/sigar_perfstat.c
+++ b/src/os/aix/perfstat/sigar_perfstat.c
@@ -6,14 +6,14 @@
  *  desired_number Must be set to 1."
  * so we just hardcode that in our wrapper.
  */
-int sigar_perfstat_cpu_total(perfstat_cpu_total_t *cpu_total, int size)
+int sigar_perfstat_cpu_total(perfstat_cpu_total_t *cpu_total, size_t size)
 {
     return perfstat_cpu_total(NULL, cpu_total, size, 1);
 }
 
 int sigar_perfstat_cpu(perfstat_id_t *id,
                        perfstat_cpu_t *cpu,
-                       int size, int num)
+                       size_t size, int num)
 {
     return perfstat_cpu(id, cpu, size, num);
 }
diff --git a/src/os/aix/sigar_os.h b/src/os/aix/sigar_os.h
index c5e3e703..28fe097a 100644
--- a/src/os/aix/sigar_os.h
+++ b/src/os/aix/sigar_os.h
@@ -27,11 +27,11 @@ typedef int (*vminfo_func_t) (void *, int, int);
 
 typedef int (*proc_fd_func_t) (sigar_t *, sigar_pid_t, sigar_proc_fd_t *);
 
-typedef int (*perfstat_cpu_total_func_t)(perfstat_cpu_total_t *, int);
+typedef int (*perfstat_cpu_total_func_t)(perfstat_cpu_total_t *, size_t);
 
 typedef int (*perfstat_cpu_func_t)(perfstat_id_t *,
                                    perfstat_cpu_t *,
-                                   int, int);
+                                   size_t, int);
 
 struct sigar_t {
     SIGAR_T_BASE;