diff --git a/include/haproxy/cpu_topo.h b/include/haproxy/cpu_topo.h
index 6a21e220e..0aa74f99e 100644
--- a/include/haproxy/cpu_topo.h
+++ b/include/haproxy/cpu_topo.h
@@ -9,6 +9,13 @@ extern int cpu_topo_maxcpus;
 extern int cpu_topo_lastcpu;
 extern struct ha_cpu_topo *ha_cpu_topo;
 
+/* Detects the CPUs that will be used based on the ones the process is bound to.
+ * Returns non-zero on success, zero on failure. Note that it may not be
+ * performed in the function above because some calls may rely on other items
+ * being allocated (e.g. trash).
+ */
+int cpu_detect_usable(void);
+
 /* Dump the CPU topology <topo> for up to cpu_topo_maxcpus CPUs for
  * debugging purposes. Offline CPUs are skipped.
  */
diff --git a/src/cpu_topo.c b/src/cpu_topo.c
index 2622994d9..dd545d50f 100644
--- a/src/cpu_topo.c
+++ b/src/cpu_topo.c
@@ -9,6 +9,31 @@ int cpu_topo_maxcpus  = -1;  // max number of CPUs supported by OS/haproxy
 int cpu_topo_lastcpu  = -1;  // last supposed online CPU (no need to look beyond)
 struct ha_cpu_topo *ha_cpu_topo = NULL;
 
+/* Detects the CPUs that will be used based on the ones the process is bound to
+ * at boot. The principle is the following: all CPUs from the boot cpuset will
+ * be used since we don't know upfront how individual threads will be mapped to
+ * groups and CPUs.
+ *
+ * Returns non-zero on success, zero on failure. Note that it may not be
+ * performed in the function above because some calls may rely on other items
+ * being allocated (e.g. trash).
+ */
+int cpu_detect_usable(void)
+{
+	struct hap_cpuset boot_set = { };
+	int cpu;
+
+	/* update the list with the CPUs currently bound to the current process */
+	ha_cpuset_detect_bound(&boot_set);
+
+	/* remove the known-excluded CPUs */
+	for (cpu = 0; cpu < cpu_topo_maxcpus; cpu++)
+		if (!ha_cpuset_isset(&boot_set, cpu))
+			ha_cpu_topo[cpu].st |= HA_CPU_F_EXCLUDED;
+
+	return 0;
+}
+
 /* Dump the CPU topology <topo> for up to cpu_topo_maxcpus CPUs for
  * debugging purposes. Offline CPUs are skipped.
  */
diff --git a/src/haproxy.c b/src/haproxy.c
index 0b36e230f..c77f88ffd 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -77,6 +77,7 @@
 #include <haproxy/connection.h>
 #ifdef USE_CPU_AFFINITY
 #include <haproxy/cpuset.h>
+#include <haproxy/cpu_topo.h>
 #endif
 #include <haproxy/debug.h>
 #include <haproxy/dns.h>
@@ -2049,6 +2050,12 @@ static void step_init_2(int argc, char** argv)
 	clock_adjust_now_offset();
 	ready_date = date;
 
+#ifdef USE_CPU_AFFINITY
+	/* we've already read the config and know what CPUs are expected
+	 * to be used. Let's check which of these are usable.
+	 */
+	cpu_detect_usable();
+#endif
 
 	/* Note: global.nbthread will be initialized as part of this call */
 	err_code |= check_config_validity();