diff --git a/doc/chrony.conf.adoc b/doc/chrony.conf.adoc
index 7db44ed..7d44937 100644
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -105,7 +105,7 @@ If the user knows that round trip delays above a certain level should cause the
 measurement to be ignored, this level can be defined with the *maxdelay*
 option. For example, *maxdelay 0.3* would indicate that measurements with a
 round-trip delay of 0.3 seconds or more should be ignored. The default value is
-3 seconds.
+3 seconds and the maximum value is 1000 seconds.
 *maxdelayratio* _ratio_:::
 This option is similar to the maxdelay option above. *chronyd* keeps a record
 of the minimum round-trip delay amongst the previous measurements that it has
diff --git a/ntp_core.c b/ntp_core.c
index a55e228..0928756 100644
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -243,6 +243,11 @@ static ARR_Instance broadcasts;
 /* Maximum acceptable delay in transmission for timestamp correction */
 #define MAX_TX_DELAY 1.0
 
+/* Maximum allowed values of maxdelay parameters */
+#define MAX_MAX_DELAY 1.0e3
+#define MAX_MAX_DELAY_RATIO 1.0e6
+#define MAX_MAX_DELAY_DEV_RATIO 1.0e6
+
 /* Minimum and maximum allowed poll interval */
 #define MIN_POLL 0
 #define MAX_POLL 24
@@ -513,9 +518,9 @@ NCR_GetInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourcePar
   if (result->presend_minpoll <= MAX_POLL && result->mode != MODE_CLIENT)
     result->presend_minpoll = MAX_POLL + 1;
 
-  result->max_delay = params->max_delay;
-  result->max_delay_ratio = params->max_delay_ratio;
-  result->max_delay_dev_ratio = params->max_delay_dev_ratio;
+  result->max_delay = CLAMP(0.0, params->max_delay, MAX_MAX_DELAY);
+  result->max_delay_ratio = CLAMP(0.0, params->max_delay_ratio, MAX_MAX_DELAY_RATIO);
+  result->max_delay_dev_ratio = CLAMP(0.0, params->max_delay_dev_ratio, MAX_MAX_DELAY_DEV_RATIO);
   result->offset_correction = params->offset;
   result->auto_offline = params->auto_offline;
   result->poll_target = params->poll_target;
@@ -2106,9 +2111,9 @@ NCR_ModifyMaxpoll(NCR_Instance inst, int new_maxpoll)
 void
 NCR_ModifyMaxdelay(NCR_Instance inst, double new_max_delay)
 {
-  inst->max_delay = new_max_delay;
+  inst->max_delay = CLAMP(0.0, new_max_delay, MAX_MAX_DELAY);
   LOG(LOGS_INFO, LOGF_NtpCore, "Source %s new max delay %f",
-      UTI_IPToString(&inst->remote_addr.ip_addr), new_max_delay);
+      UTI_IPToString(&inst->remote_addr.ip_addr), inst->max_delay);
 }
 
 /* ================================================== */
@@ -2116,9 +2121,9 @@ NCR_ModifyMaxdelay(NCR_Instance inst, double new_max_delay)
 void
 NCR_ModifyMaxdelayratio(NCR_Instance inst, double new_max_delay_ratio)
 {
-  inst->max_delay_ratio = new_max_delay_ratio;
+  inst->max_delay_ratio = CLAMP(0.0, new_max_delay_ratio, MAX_MAX_DELAY_RATIO);
   LOG(LOGS_INFO, LOGF_NtpCore, "Source %s new max delay ratio %f",
-      UTI_IPToString(&inst->remote_addr.ip_addr), new_max_delay_ratio);
+      UTI_IPToString(&inst->remote_addr.ip_addr), inst->max_delay_ratio);
 }
 
 /* ================================================== */
@@ -2126,9 +2131,9 @@ NCR_ModifyMaxdelayratio(NCR_Instance inst, double new_max_delay_ratio)
 void
 NCR_ModifyMaxdelaydevratio(NCR_Instance inst, double new_max_delay_dev_ratio)
 {
-  inst->max_delay_dev_ratio = new_max_delay_dev_ratio;
+  inst->max_delay_dev_ratio = CLAMP(0.0, new_max_delay_dev_ratio, MAX_MAX_DELAY_DEV_RATIO);
   LOG(LOGS_INFO, LOGF_NtpCore, "Source %s new max delay dev ratio %f",
-      UTI_IPToString(&inst->remote_addr.ip_addr), new_max_delay_dev_ratio);
+      UTI_IPToString(&inst->remote_addr.ip_addr), inst->max_delay_dev_ratio);
 }
 
 /* ================================================== */