diff --git a/configure.ac b/configure.ac
index 9773993..2678f64 100644
--- a/configure.ac
+++ b/configure.ac
@@ -68,7 +68,7 @@ AC_SYS_LARGEFILE
 AC_FUNC_MALLOC
 AC_FUNC_REALLOC
 AC_FUNC_STRTOD
-AC_CHECK_FUNCS([memchr memmove memset strerror strtol])
+AC_CHECK_FUNCS([memchr memmove memset strerror strtol sched_getaffinity])
 AC_CHECK_HEADER([sys/endian.h],
                [
                  AC_CHECK_DECLS([htole64, le64toh], [], [], [
diff --git a/src/cpu.c b/src/cpu.c
index c0155ef..3d2e813 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -1,5 +1,28 @@
+#define _GNU_SOURCE
+
 #include <unistd.h>
 
+#include "config.h"
+
+#ifdef HAVE_SCHED_GETAFFINITY
+
+#include <sched.h>
+#include <stdio.h>
+
+size_t num_threads(void) {
+    cpu_set_t cpu_set;
+    CPU_ZERO(&cpu_set);
+
+    if (sched_getaffinity(0, sizeof cpu_set, &cpu_set) == -1)
+        return sysconf(_SC_NPROCESSORS_ONLN);
+    else
+        return CPU_COUNT(&cpu_set);
+}
+
+#else
+
 size_t num_threads(void) {
     return sysconf(_SC_NPROCESSORS_ONLN);
 }
+
+#endif