diff --git a/NEWS b/NEWS
index 8ac7e1fcb8..1c6d756fed 100644
--- a/NEWS
+++ b/NEWS
@@ -27,6 +27,8 @@ New Functionality
 - Geneve tunnel options of the current packet can be extracted from scripts
   using the new PacketAnalyzer::Geneve::get_options() builtin function.
 
+- The new ``is_valid_subnet()`` function mirrors ``is_valid_ip()``, for subnets.
+
 Changed Functionality
 ---------------------
 
diff --git a/src/script_opt/FuncInfo.cc b/src/script_opt/FuncInfo.cc
index 50d17440ca..be25a66a8f 100644
--- a/src/script_opt/FuncInfo.cc
+++ b/src/script_opt/FuncInfo.cc
@@ -353,6 +353,7 @@ static std::unordered_map<std::string, unsigned int> func_attrs = {
     {"is_v6_addr", ATTR_FOLDABLE},
     {"is_v6_subnet", ATTR_FOLDABLE},
     {"is_valid_ip", ATTR_FOLDABLE},
+    {"is_valid_subnet", ATTR_FOLDABLE},
     {"join_string_set", ATTR_FOLDABLE},
     {"join_string_vec", ATTR_FOLDABLE},
     {"levenshtein_distance", ATTR_FOLDABLE},
diff --git a/src/zeek.bif b/src/zeek.bif
index 3a7bb3644b..e97c988d39 100644
--- a/src/zeek.bif
+++ b/src/zeek.bif
@@ -2831,10 +2831,17 @@ function to_addr%(ip: string%): addr
 ## Returns: T if the string is a valid IPv4 or IPv6 address format.
 function is_valid_ip%(ip: string%): bool
 	%{
-	char* s = ip->AsString()->Render();
-	auto rval = zeek::IPAddr::IsValid(s);
-	delete [] s;
-	return zeek::val_mgr->Bool(rval);
+	return zeek::val_mgr->Bool(zeek::IPAddr::IsValid(ip->ToStdString().c_str()));
+	%}
+
+## Checks if a string is a valid IPv4 or IPv6 subnet.
+##
+## cidr: the string to check for valid subnet formatting.
+##
+## Returns: T if the string is a valid IPv4 or IPv6 subnet format.
+function is_valid_subnet%(cidr: string%): bool
+	%{
+	return zeek::val_mgr->Bool(zeek::IPPrefix::IsValid(cidr->ToStdString().c_str()));
 	%}
 
 ## Converts a :zeek:type:`string` to a :zeek:type:`subnet`.
diff --git a/testing/btest/Baseline/opt.ZAM-bif-tracking/output b/testing/btest/Baseline/opt.ZAM-bif-tracking/output
index 972665cbdb..3c90b8960c 100644
--- a/testing/btest/Baseline/opt.ZAM-bif-tracking/output
+++ b/testing/btest/Baseline/opt.ZAM-bif-tracking/output
@@ -1,2 +1,2 @@
 ### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
-556 seen BiFs, 0 unseen BiFs (), 0 new BiFs ()
+557 seen BiFs, 0 unseen BiFs (), 0 new BiFs ()
diff --git a/testing/btest/Baseline/scripts.base.utils.addrs/output b/testing/btest/Baseline/scripts.base.utils.addrs/output
index 622edef994..c64ea7defb 100644
--- a/testing/btest/Baseline/scripts.base.utils.addrs/output
+++ b/testing/btest/Baseline/scripts.base.utils.addrs/output
@@ -48,6 +48,16 @@ F
 F
 F
 F
+============ test is_valid_subnet()
+T
+T
+T
+T
+F
+F
+F
+F
+F
 ============ test extract_ip_addresses()
 [1.1.1.1, 2.2.2.2, 3.3.3.3]
 [1.1.1.1, 0:0:0:0:0:0:0:0, 3.3.3.3]
diff --git a/testing/btest/opt/ZAM-bif-tracking.zeek b/testing/btest/opt/ZAM-bif-tracking.zeek
index 1d11c555c5..b57e55e762 100644
--- a/testing/btest/opt/ZAM-bif-tracking.zeek
+++ b/testing/btest/opt/ZAM-bif-tracking.zeek
@@ -386,6 +386,7 @@ global known_BiFs = set(
 	"is_v6_addr",
 	"is_v6_subnet",
 	"is_valid_ip",
+	"is_valid_subnet",
 	"join_string_set",
 	"join_string_vec",
 	"levenshtein_distance",
diff --git a/testing/btest/scripts/base/utils/addrs.test b/testing/btest/scripts/base/utils/addrs.test
index e0bc384fad..68dcdaf4d3 100644
--- a/testing/btest/scripts/base/utils/addrs.test
+++ b/testing/btest/scripts/base/utils/addrs.test
@@ -132,6 +132,17 @@ event zeek_init()
 	print is_valid_ip("6:1:2::3:4:5:6:7");
 	print is_valid_ip("6:1:2::3:4:5:6:7:8");
 
+	print "============ test is_valid_subnet()";
+	print is_valid_subnet("10.0.0.0/0"); # T!
+	print is_valid_subnet("10.0.0.0/8");
+	print is_valid_subnet("10.0.0.0/32");
+	print is_valid_subnet("fe80::/64");
+	print is_valid_subnet("10.0.0.0/64"); # F
+	print is_valid_subnet("256.256.256.256/32"); # F
+	print is_valid_subnet("10.0.0.0"); # F
+	print is_valid_subnet("[fe80::]/64"); # F
+	print is_valid_subnet("10/8"); # F
+
 	print "============ test extract_ip_addresses()";
 	print extract_ip_addresses("this is 1.1.1.1 a test 2.2.2.2 string with ip addresses 3.3.3.3");
 	print extract_ip_addresses("this is 1.1.1.1 a test 0:0:0:0:0:0:0:0 string with ip addresses 3.3.3.3");