diff --git a/CHANGES b/CHANGES
index 4e17e0333e..cdf0f42017 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+3934.	[bug]		Catch bad 'sit-secret' in named-checkconf.  Improve
+			sit-secrets documentation. [RT #36980]
+
 3933.	[bug]		Corrected the implementation of dns_rdata_casecompare()
 			for the HIP rdata type.  [RT #36911]
 
diff --git a/bin/tests/system/sit/bad-sit-badhex.conf b/bin/tests/system/sit/bad-sit-badhex.conf
new file mode 100644
index 0000000000..6b84d8a6a1
--- /dev/null
+++ b/bin/tests/system/sit/bad-sit-badhex.conf
@@ -0,0 +1,3 @@
+options {
+	sit-secret "012345678901234567890123456789012345678901234567890123456789012";
+};
diff --git a/bin/tests/system/sit/bad-sit-toolong.conf b/bin/tests/system/sit/bad-sit-toolong.conf
new file mode 100644
index 0000000000..aec4d252c8
--- /dev/null
+++ b/bin/tests/system/sit/bad-sit-toolong.conf
@@ -0,0 +1,3 @@
+options {
+	sit-secret "01234567890123456789012345678901234567890123456789012345678901234567890";
+};
diff --git a/bin/tests/system/sit/tests.sh b/bin/tests/system/sit/tests.sh
index fa1a71abb0..5842a98714 100755
--- a/bin/tests/system/sit/tests.sh
+++ b/bin/tests/system/sit/tests.sh
@@ -32,6 +32,15 @@ havetc() {
 	grep 'flags:.* tc[^;]*;' $1 > /dev/null
 }
 
+for bad in bad*.conf
+do
+        ret=0
+        echo "I:checking that named-checkconf detects error in $bad"
+        $CHECKCONF $bad > /dev/null 2>&1
+        if [ $? != 1 ]; then echo "I:failed"; ret=1; fi
+        status=`expr $status + $ret`
+done
+
 n=`expr $n + 1`
 echo "I:checking SIT token returned to empty SIT option ($n)"
 ret=0
diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 7562a331ed..01f2c207c3 100644
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -6421,12 +6421,16 @@ options {
 	    </varlistentry>
 
 	    <varlistentry>
-	      <term><command>sit-secret</command></term> <listitem>
+	      <term><command>sit-secret</command></term>
+	      <listitem>
 		<para>
 		  If set, this is a shared secret used for generating
 		  and verifying Source Identity Token EDNS options
 		  within a anycast cluster.  If not set the system
-		  will generate a random secret at startup.
+		  will generate a random secret at startup.  The
+		  shared secret is encoded as a hex string and needs
+		  to be 128 bits for AES128, 160 bits for SHA1 and
+		  256 bits for SHA256.
 		</para>
 	      </listitem>
 	    </varlistentry>
diff --git a/lib/bind9/check.c b/lib/bind9/check.c
index a8d5e00aa6..38c1b244ed 100644
--- a/lib/bind9/check.c
+++ b/lib/bind9/check.c
@@ -24,10 +24,12 @@
 #include <isc/base64.h>
 #include <isc/buffer.h>
 #include <isc/file.h>
+#include <isc/hex.h>
 #include <isc/log.h>
 #include <isc/mem.h>
 #include <isc/netaddr.h>
 #include <isc/parseint.h>
+#include <isc/platform.h>
 #include <isc/region.h>
 #include <isc/result.h>
 #include <isc/sockaddr.h>
@@ -35,6 +37,18 @@
 #include <isc/symtab.h>
 #include <isc/util.h>
 
+#ifdef ISC_PLATFORM_USESIT
+#ifdef AES_SIT
+#include <isc/aes.h>
+#endif
+#ifdef HMAC_SHA1_SIT
+#include <isc/sha1.h>
+#endif
+#ifdef HMAC_SHA256_SIT
+#include <isc/sha2.h>
+#endif
+#endif
+
 #include <dns/acl.h>
 #include <dns/fixedname.h>
 #include <dns/rdataclass.h>
@@ -1186,6 +1200,52 @@ check_options(const cfg_obj_t *options, isc_log_t *logctx, isc_mem_t *mctx,
 				    "(%d seconds)", recheck, lifetime);
 	}
 
+#ifdef ISC_PLATFORM_USESIT
+        obj = NULL;
+        (void) cfg_map_get(options, "sit-secret", &obj);
+        if (obj != NULL) {
+                isc_buffer_t b;
+		unsigned char secret[32];
+
+                memset(secret, 0, sizeof(secret));
+                isc_buffer_init(&b, secret, sizeof(secret));
+                tresult = isc_hex_decodestring(cfg_obj_asstring(obj), &b);
+		if (tresult == ISC_R_NOSPACE) {	
+			cfg_obj_log(obj, logctx, ISC_LOG_ERROR,
+				    "sit-secret: too long");
+		} else if (tresult != ISC_R_SUCCESS) {
+			cfg_obj_log(obj, logctx, ISC_LOG_ERROR,
+				    "sit-secret: invalid hex string");
+		}
+		if (tresult != ISC_R_SUCCESS)
+			result = tresult;
+#ifdef AES_SIT
+                if (tresult == ISC_R_SUCCESS &&
+		    isc_buffer_usedlength(&b) != ISC_AES128_KEYLENGTH) {
+			cfg_obj_log(obj, logctx, ISC_LOG_ERROR,
+                                    "AES sit-secret must be on 128 bits");
+			result = ISC_R_RANGE;
+		}
+#endif
+#ifdef HMAC_SHA1_SIT
+                if (tresult == ISC_R_SUCCESS &&
+		    isc_buffer_usedlength(&b) != ISC_SHA1_DIGESTLENGTH) {
+			cfg_obj_log(obj, logctx, ISC_LOG_ERROR,
+				    "SHA1 sit-secret must be on 160 bits");
+			result = ISC_R_RANGE;
+		}
+#endif
+#ifdef HMAC_SHA256_SIT
+                if (tresult == ISC_R_SUCCESS &&
+		    isc_buffer_usedlength(&b) != ISC_SHA256_DIGESTLENGTH) {
+			cfg_obj_log(obj, logctx, ISC_LOG_ERROR,
+                                    "SHA256 sit-secret must be on 256 bits");
+			result = ISC_R_RANGE;
+		}
+#endif
+        }
+#endif
+
 	return (result);
 }