diff --git a/CHANGES b/CHANGES
index c8b87d68c3..dabcb33d0c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+4.1.0-dev.669 | 2021-06-01 09:39:30 -0700
+
+  * GH-839: Fix use of &optional sub-records within table/set indices (Jon Siwek, Corelight)
+
 4.1.0-dev.666 | 2021-05-26 10:51:51 -0700
 
   * Ensure SessionAdapter members are initialized (Tim Wojtulewicz, Corelight)
diff --git a/VERSION b/VERSION
index b7a018b454..4c068bef23 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-4.1.0-dev.666
+4.1.0-dev.669
diff --git a/src/CompHash.cc b/src/CompHash.cc
index de5bb5fbc7..cd556017cc 100644
--- a/src/CompHash.cc
+++ b/src/CompHash.cc
@@ -509,6 +509,9 @@ int CompositeHash::SingleTypeKeySize(Type* bt, const Val* v,
 
 		case TYPE_RECORD:
 			{
+			if ( ! v )
+				return (optional && ! calc_static_size) ? sz : 0;
+
 			const RecordVal* rv = v ? v->AsRecordVal() : nullptr;
 			RecordType* rt = bt->AsRecordType();
 			int num_fields = rt->NumFields();
diff --git a/testing/btest/Baseline/language.table-optional-subrecord-index/out b/testing/btest/Baseline/language.table-optional-subrecord-index/out
new file mode 100644
index 0000000000..86505abdf5
--- /dev/null
+++ b/testing/btest/Baseline/language.table-optional-subrecord-index/out
@@ -0,0 +1,18 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+2, {
+[subrec=[str=hi]],
+[subrec=<uninitialized>]
+}
+T
+T
+T
+T
+T
+0, {
+
+}
+T
+T
+T
+T
+T
diff --git a/testing/btest/language/table-optional-subrecord-index.zeek b/testing/btest/language/table-optional-subrecord-index.zeek
new file mode 100644
index 0000000000..9731ca41f5
--- /dev/null
+++ b/testing/btest/language/table-optional-subrecord-index.zeek
@@ -0,0 +1,35 @@
+# @TEST-EXEC: zeek -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+# @TEST-DOC: Check functionality of a table/set index consisting of optional sub-records.
+
+type SubRec: record {
+	str: string;
+};
+
+type Rec: record {
+	subrec: SubRec &optional;
+};
+
+global myset: set[Rec] = set();
+
+local i = Rec();
+local j = Rec($subrec=SubRec($str="hi"));
+add myset[i];
+add myset[j];
+print |myset|, myset;
+
+# All membership tests below are expected to evaluate to true.
+print i in myset;
+print j in myset;
+print Rec() in myset;
+print Rec($subrec=SubRec($str="hi")) in myset;
+print Rec($subrec=SubRec($str="no")) !in myset;
+
+delete myset[i];
+delete myset[j];
+print |myset|, myset;
+print i !in myset;
+print j !in myset;
+print Rec() !in myset;
+print Rec($subrec=SubRec($str="hi")) !in myset;
+print Rec($subrec=SubRec($str="no")) !in myset;