diff --git a/src/Val.cc b/src/Val.cc
index cbc883347c..bf86360b70 100644
--- a/src/Val.cc
+++ b/src/Val.cc
@@ -996,11 +996,17 @@ static std::variant<ValPtr, std::string> BuildVal(const rapidjson::Value& j, con
                 return mismatch_err();
 
             std::string candidate(j.GetString(), j.GetStringLength());
+            // Remove any surrounding '/'s, not needed when creating an RE_matcher.
             if ( candidate.size() > 2 && candidate.front() == candidate.back() && candidate.back() == '/' ) {
-                // Remove the '/'s
                 candidate.erase(0, 1);
                 candidate.erase(candidate.size() - 1);
             }
+            // Remove any surrounding "^?(" and ")$?", automatically added below.
+            if ( candidate.size() > 6 && candidate.substr(0, 3) == "^?(" &&
+                 candidate.substr(candidate.size() - 3, 3) == ")$?" ) {
+                candidate.erase(0, 3);
+                candidate.erase(candidate.size() - 3);
+            }
 
             auto re = std::make_unique<RE_Matcher>(candidate.c_str());
             if ( ! re->Compile() )
diff --git a/testing/btest/Baseline/language.set/out b/testing/btest/Baseline/language.set/out
index 51d2a72711..c53cae332c 100644
--- a/testing/btest/Baseline/language.set/out
+++ b/testing/btest/Baseline/language.set/out
@@ -76,18 +76,26 @@ table index membership (PASS)
 table index non-membership (PASS)
 table index reduced size (PASS)
 table index iteration (PASS)
+table index JSON roundtrip success (PASS)
+table index JSON roundtrip correct (PASS)
 vector index size (PASS)
 vector index membership (PASS)
 vector index non-membership (PASS)
 vector index reduced size (PASS)
 vector index iteration (PASS)
+vector index JSON roundtrip success (PASS)
+vector index JSON roundtrip correct (PASS)
 set index size (PASS)
 set index membership (PASS)
 set index non-membership (PASS)
 set index reduced size (PASS)
 set index iteration (PASS)
+set index JSON roundtrip success (PASS)
+set index JSON roundtrip correct (PASS)
 pattern index size (PASS)
 pattern index membership (PASS)
 pattern index non-membership (PASS)
 pattern index reduced size (PASS)
 pattern index iteration (PASS)
+pattern index JSON roundtrip success (PASS)
+pattern index JSON roundtrip correct (PASS)
diff --git a/testing/btest/language/set.zeek b/testing/btest/language/set.zeek
index 110856a7b4..24e2ce402c 100644
--- a/testing/btest/language/set.zeek
+++ b/testing/btest/language/set.zeek
@@ -186,82 +186,119 @@ function basic_functionality()
 	test_case( "magnitude", |a_and_b| == |a_or_b|);
 }
 
-function complex_index_types()
+type tss_set: set[table[string] of string];
+
+function complex_index_type_table()
 {
 	# Initialization
-	local s1: set[table[string] of string] = { table(["k1"] = "v1") };
+	local s: tss_set = { table(["k1"] = "v1") };
 
 	# Adding a member
-	add s1[table(["k2"] = "v2")];
+	add s[table(["k2"] = "v2")];
 
 	# Various checks, including membership test
-	test_case( "table index size", |s1| == 2 );
-	test_case( "table index membership", table(["k2"] = "v2") in s1 );
-	test_case( "table index non-membership", table(["k2"] = "v3") !in s1 );
+	test_case( "table index size", |s| == 2 );
+	test_case( "table index membership", table(["k2"] = "v2") in s );
+	test_case( "table index non-membership", table(["k2"] = "v3") !in s );
 
 	# Member deletion
-	delete s1[table(["k1"] = "v1")];
-	test_case( "table index reduced size", |s1| == 1 );
+	delete s[table(["k1"] = "v1")];
+	test_case( "table index reduced size", |s| == 1 );
 
 	# Iteration
-	for ( ti in s1 )
+	for ( ti in s )
 		{
 		test_case( "table index iteration", to_json(ti) == to_json(table(["k2"] = "v2")) );
 		break;
 		}
 
+	# JSON serialize/unserialize
+	local fjr = from_json(to_json(s), tss_set);
+	test_case( "table index JSON roundtrip success", fjr$valid );
+	test_case( "table index JSON roundtrip correct", to_json(s) == to_json(fjr$v) );
+}
+
+type vs_set: set[vector of string];
+
+function complex_index_type_vector()
+{
 	# As above, for other index types
-	local s2: set[vector of string] = { vector("v1", "v2") };
+	local s: vs_set = { vector("v1", "v2") };
 
-	add s2[vector("v3", "v4")];
-	test_case( "vector index size", |s2| == 2 );
-	test_case( "vector index membership", vector("v3", "v4") in s2 );
-	test_case( "vector index non-membership", vector("v4", "v5") !in s2 );
+	add s[vector("v3", "v4")];
+	test_case( "vector index size", |s| == 2 );
+	test_case( "vector index membership", vector("v3", "v4") in s );
+	test_case( "vector index non-membership", vector("v4", "v5") !in s );
 
-	delete s2[vector("v1", "v2")];
-	test_case( "vector index reduced size", |s2| == 1 );
+	delete s[vector("v1", "v2")];
+	test_case( "vector index reduced size", |s| == 1 );
 
-	for ( vi in s2 )
+	for ( vi in s )
 		{
 		test_case( "vector index iteration", to_json(vi) == to_json(vector("v3", "v4")) );
 		break;
 		}
 
-	local s3: set[set[string]] = { set("s1", "s2") };
+	local fjr = from_json(to_json(s), vs_set);
+	test_case( "vector index JSON roundtrip success", fjr$valid );
+	test_case( "vector index JSON roundtrip correct", to_json(s) == to_json(fjr$v) );
+}
 
-	add s3[set("s3", "s4")];
-	test_case( "set index size", |s3| == 2 );
-	test_case( "set index membership", set("s3", "s4") in s3 );
-	test_case( "set index non-membership", set("s4", "s5") !in s3 );
+type ss_set: set[set[string]];
 
-	delete s3[set("s1", "s2")];
-	test_case( "set index reduced size", |s3| == 1 );
+function complex_index_type_set()
+{
+	local s: ss_set = { set("s1", "s2") };
 
-	for ( si in s3 )
+	add s[set("s3", "s4")];
+	test_case( "set index size", |s| == 2 );
+	test_case( "set index membership", set("s3", "s4") in s );
+	test_case( "set index non-membership", set("s4", "s5") !in s );
+
+	delete s[set("s1", "s2")];
+	test_case( "set index reduced size", |s| == 1 );
+
+	for ( si in s )
 		{
 		test_case( "set index iteration", to_json(si) == to_json(set("s3", "s4")) );
 		break;
 		}
 
-	local s4: set[pattern] = { /pat1/ };
+	local fjr = from_json(to_json(s), ss_set);
+	test_case( "set index JSON roundtrip success", fjr$valid );
+	test_case( "set index JSON roundtrip correct", to_json(s) == to_json(fjr$v) );
+}
 
-	add s4[/pat2/];
-	test_case( "pattern index size", |s4| == 2 );
-	test_case( "pattern index membership", /pat2/ in s4 );
-	test_case( "pattern index non-membership", /pat3/ !in s4 );
+type p_set: set[pattern];
 
-	delete s4[/pat1/];
-	test_case( "pattern index reduced size", |s4| == 1 );
+function complex_index_type_pattern()
+{
+	local s: p_set = { /pat1/ };
 
-	for ( pi in s4 )
+	add s[/pat2/];
+	test_case( "pattern index size", |s| == 2 );
+	test_case( "pattern index membership", /pat2/ in s );
+	test_case( "pattern index non-membership", /pat3/ !in s );
+
+	delete s[/pat1/];
+	test_case( "pattern index reduced size", |s| == 1 );
+
+	for ( pi in s )
 		{
 		test_case( "pattern index iteration", to_json(pi) == to_json(/pat2/) );
 		break;
 		}
+
+	local fjr = from_json(to_json(s), p_set);
+	test_case( "pattern index JSON roundtrip success", fjr$valid );
+	test_case( "pattern index JSON roundtrip correct", to_json(s) == to_json(fjr$v) );
 }
 
 event zeek_init()
 {
 	basic_functionality();
-	complex_index_types();
+	complex_index_type_table();
+	complex_index_type_vector();
+	complex_index_type_set();
+	complex_index_type_pattern();
 }