diff --git a/lib/isccfg/duration.c b/lib/isccfg/duration.c
index 0a7501b022..27dddca1cc 100644
--- a/lib/isccfg/duration.c
+++ b/lib/isccfg/duration.c
@@ -28,6 +28,8 @@
 #include <isc/string.h>
 #include <isc/util.h>
 
+#include <dns/ttl.h>
+
 #include <isccfg/duration.h>
 
 /*
@@ -153,3 +155,48 @@ isccfg_duration_fromtext(isc_textregion_t *source,
 	duration->iso8601 = true;
 	return (ISC_R_SUCCESS);
 }
+
+isc_result_t
+isccfg_parse_duration(isc_textregion_t *source, isccfg_duration_t *duration) {
+	isc_result_t result;
+
+	REQUIRE(duration != NULL);
+
+	duration->unlimited = false;
+	result = isccfg_duration_fromtext(source, duration);
+	if (result == ISC_R_BADNUMBER) {
+		/* Fallback to dns_ttl_fromtext. */
+		uint32_t ttl;
+		result = dns_ttl_fromtext(source, &ttl);
+		if (result == ISC_R_SUCCESS) {
+			/*
+			 * With dns_ttl_fromtext() the information on optional
+			 * units is lost, and is treated as seconds from now on.
+			 */
+			duration->iso8601 = false;
+			duration->parts[6] = ttl;
+		}
+	}
+
+	return (result);
+}
+
+uint32_t
+isccfg_duration_toseconds(const isccfg_duration_t *duration) {
+	uint32_t seconds = 0;
+
+	REQUIRE(duration != NULL);
+
+	seconds += duration->parts[6];		   /* Seconds */
+	seconds += duration->parts[5] * 60;	   /* Minutes */
+	seconds += duration->parts[4] * 3600;	   /* Hours */
+	seconds += duration->parts[3] * 86400;	   /* Days */
+	seconds += duration->parts[2] * 86400 * 7; /* Weeks */
+	/*
+	 * The below additions are not entirely correct
+	 * because days may very per month and per year.
+	 */
+	seconds += duration->parts[1] * 86400 * 31;  /* Months */
+	seconds += duration->parts[0] * 86400 * 365; /* Years */
+	return (seconds);
+}
diff --git a/lib/isccfg/include/isccfg/duration.h b/lib/isccfg/include/isccfg/duration.h
index 32b23e4342..b64bea520f 100644
--- a/lib/isccfg/include/isccfg/duration.h
+++ b/lib/isccfg/include/isccfg/duration.h
@@ -55,4 +55,29 @@ isccfg_duration_fromtext(isc_textregion_t *source, isccfg_duration_t *duration);
  *\li	DNS_R_BADNUMBER
  */
 
+isc_result_t
+isccfg_parse_duration(isc_textregion_t *source, isccfg_duration_t *duration);
+/*%<
+ * Converts a duration string to a ISO 8601 duration.
+ * If the string does not start with a P (or p), fall back to TTL-style value.
+ * In that case the duration will be treated in seconds only.
+ *
+ * Returns:
+ *\li	ISC_R_SUCCESS
+ *\li	DNS_R_BADNUMBER
+ *\li	DNS_R_BADTTL
+ */
+
+uint32_t
+isccfg_duration_toseconds(const isccfg_duration_t *duration);
+/*%<
+ * Converts an ISO 8601 duration to seconds.
+ * The conversion is approximate:
+ * - Months will be treated as 31 days.
+ * - Years will be treated as 365 days.
+ *
+ * Returns:
+ *\li	The duration in seconds.
+ */
+
 ISC_LANG_ENDDECLS
diff --git a/lib/isccfg/kaspconf.c b/lib/isccfg/kaspconf.c
index 7c476b1a68..a0460ff968 100644
--- a/lib/isccfg/kaspconf.c
+++ b/lib/isccfg/kaspconf.c
@@ -65,20 +65,9 @@ parse_duration(const char *str) {
 
 	DE_CONST(str, tr.base);
 	tr.length = strlen(tr.base);
-	result = isccfg_duration_fromtext(&tr, &duration);
-	if (result == ISC_R_BADNUMBER) {
-		/* Fallback to dns_ttl_fromtext. */
-		(void)dns_ttl_fromtext(&tr, &time);
-		return (time);
-	}
+	result = isccfg_parse_duration(&tr, &duration);
 	if (result == ISC_R_SUCCESS) {
-		time += duration.parts[6];		 /* Seconds */
-		time += duration.parts[5] * 60;		 /* Minutes */
-		time += duration.parts[4] * 3600;	 /* Hours */
-		time += duration.parts[3] * 86400;	 /* Days */
-		time += duration.parts[2] * 86400 * 7;	 /* Weaks */
-		time += duration.parts[1] * 86400 * 31;	 /* Months */
-		time += duration.parts[0] * 86400 * 365; /* Years */
+		time = isccfg_duration_toseconds(&duration);
 	}
 	return (time);
 }
diff --git a/lib/isccfg/parser.c b/lib/isccfg/parser.c
index db2a328c2a..4ea849e64f 100644
--- a/lib/isccfg/parser.c
+++ b/lib/isccfg/parser.c
@@ -1139,19 +1139,7 @@ cfg_obj_isduration(const cfg_obj_t *obj) {
 uint32_t
 cfg_obj_asduration(const cfg_obj_t *obj) {
 	REQUIRE(obj != NULL && obj->type->rep == &cfg_rep_duration);
-	uint32_t duration = 0;
-	duration += obj->value.duration.parts[6];	      /* Seconds */
-	duration += obj->value.duration.parts[5] * 60;	      /* Minutes */
-	duration += obj->value.duration.parts[4] * 3600;      /* Hours */
-	duration += obj->value.duration.parts[3] * 86400;     /* Days */
-	duration += obj->value.duration.parts[2] * 86400 * 7; /* Weaks */
-	/*
-	 * The below additions are not entirely correct
-	 * because days may very per month and per year.
-	 */
-	duration += obj->value.duration.parts[1] * 86400 * 31;	/* Months */
-	duration += obj->value.duration.parts[0] * 86400 * 365; /* Years */
-	return (duration);
+	return isccfg_duration_toseconds(&(obj->value.duration));
 }
 
 static isc_result_t
@@ -1160,24 +1148,9 @@ parse_duration(cfg_parser_t *pctx, cfg_obj_t **ret) {
 	cfg_obj_t *obj = NULL;
 	isccfg_duration_t duration;
 
-	duration.unlimited = false;
-
-	result = isccfg_duration_fromtext(&pctx->token.value.as_textregion,
+	result = isccfg_parse_duration(&pctx->token.value.as_textregion,
 				       &duration);
-	if (result == ISC_R_BADNUMBER) {
-		/* Fallback to dns_ttl_fromtext. */
-		uint32_t ttl;
-		result = dns_ttl_fromtext(&pctx->token.value.as_textregion,
-					  &ttl);
-		if (result == ISC_R_SUCCESS) {
-			/*
-			 * With dns_ttl_fromtext() the information on optional
-			 * units is lost, and is treated as seconds from now on.
-			 */
-			duration.iso8601 = false;
-			duration.parts[6] = ttl;
-		}
-	}
+
 	if (result == ISC_R_RANGE) {
 		cfg_parser_error(pctx, CFG_LOG_NEAR,
 				 "duration or TTL out of range");