diff --git a/CHANGES b/CHANGES
index 32a05e1e5f..077b0e452f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,9 @@
+7.1.0-dev.40 | 2024-07-24 11:18:03 +0200
+
+  * minor optimization of boolean comparisons (Vern Paxson, Corelight)
+
+  * GH-3839: fix & regression test for GH-3839 (spurious warnings for "when" constructs) (Vern Paxson, Corelight)
+
 7.1.0-dev.37 | 2024-07-23 19:18:37 -0700
 
   * Bump zeek-testing-cluster to reflect deprecation of prometheus.zeek (Christian Kreibich, Corelight)
diff --git a/VERSION b/VERSION
index e0a1592835..cc218b636a 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-7.1.0-dev.37
+7.1.0-dev.40
diff --git a/src/Func.cc b/src/Func.cc
index 87783a30a9..85d184295d 100644
--- a/src/Func.cc
+++ b/src/Func.cc
@@ -434,7 +434,7 @@ ValPtr ScriptFunc::Invoke(zeek::Args* args, Frame* parent) const {
 
     // Warn if the function returns something, but we returned from
     // the function without an explicit return, or without a value.
-    else if ( GetType()->Yield() && GetType()->Yield()->Tag() != TYPE_VOID &&
+    else if ( GetType()->Yield() && GetType()->Yield()->Tag() != TYPE_VOID && ! GetType()->ExpressionlessReturnOkay() &&
               (flow != FLOW_RETURN /* we fell off the end */ || ! result /* explicit return with no result */) &&
               ! f->HasDelayed() )
         reporter->Warning("non-void function returning without a value: %s", Name());
diff --git a/src/script_opt/Expr.cc b/src/script_opt/Expr.cc
index 1ad24c5277..353604f1a7 100644
--- a/src/script_opt/Expr.cc
+++ b/src/script_opt/Expr.cc
@@ -1238,10 +1238,28 @@ ExprPtr EqExpr::Reduce(Reducer* c, StmtPtr& red_stmt) {
     if ( IsHasElementsTest() )
         return BuildHasElementsTest()->Reduce(c, red_stmt);
 
-    if ( GetType()->Tag() == TYPE_BOOL && same_singletons(op1, op2) ) {
-        bool t = Tag() == EXPR_EQ;
-        auto res = with_location_of(make_intrusive<ConstExpr>(val_mgr->Bool(t)), this);
-        return res->Reduce(c, red_stmt);
+    if ( GetType()->Tag() == TYPE_BOOL ) {
+        if ( same_singletons(op1, op2) ) {
+            bool t = Tag() == EXPR_EQ;
+            auto res = with_location_of(make_intrusive<ConstExpr>(val_mgr->Bool(t)), this);
+            return res->Reduce(c, red_stmt);
+        }
+
+        if ( op1->GetType()->Tag() == TYPE_BOOL ) {
+            if ( op1->Tag() == EXPR_CONST )
+                std::swap(op1, op2);
+
+            if ( op2->Tag() == EXPR_CONST ) {
+                bool t = Tag() == EXPR_EQ;
+                if ( op2->AsConstExpr()->Value()->IsZero() )
+                    t = ! t;
+                if ( t )
+                    return op1->Reduce(c, red_stmt);
+
+                auto res = with_location_of(make_intrusive<NotExpr>(op1), this);
+                return res->Reduce(c, red_stmt);
+            }
+        }
     }
 
     return BinaryExpr::Reduce(c, red_stmt);
diff --git a/src/script_opt/Stmt.cc b/src/script_opt/Stmt.cc
index 618d52ebda..8ef72c60b4 100644
--- a/src/script_opt/Stmt.cc
+++ b/src/script_opt/Stmt.cc
@@ -245,6 +245,12 @@ StmtPtr IfStmt::DoReduce(Reducer* c) {
             red_e_stmt = cond_red_stmt;
     }
 
+    // Check again for negation given above reductions/replacements.
+    if ( e->Tag() == EXPR_NOT ) {
+        std::swap(s1, s2);
+        e = e->GetOp1();
+    }
+
     StmtPtr sl;
 
     if ( e->IsConst() ) {
diff --git a/testing/btest/Baseline/language.when/out b/testing/btest/Baseline/language.when/out
index 07f8c832ca..5e61f7ed4b 100644
--- a/testing/btest/Baseline/language.when/out
+++ b/testing/btest/Baseline/language.when/out
@@ -1,3 +1,4 @@
 ### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
 done
 lookup successful
+received termination signal
diff --git a/testing/btest/language/when.zeek b/testing/btest/language/when.zeek
index d0d07b44fa..e32785abc7 100644
--- a/testing/btest/language/when.zeek
+++ b/testing/btest/language/when.zeek
@@ -1,6 +1,6 @@
 # @TEST-EXEC: btest-bg-run test1 zeek -b %INPUT
 # @TEST-EXEC: btest-bg-wait 10
-# @TEST-EXEC: mv test1/.stdout out
+# @TEST-EXEC: cat test1/.stdout test1/.stderr >> out
 # @TEST-EXEC: btest-diff out
 
 redef exit_only_after_terminate = T;
@@ -26,6 +26,13 @@ event zeek_init()
 	when [h] ( local hname3 = lookup_addr(h) ) {}
 	timeout to + 2sec {}
 
+	# The following used to generate a spurious warning, so it's here
+	# as a regression test.
+	when ( local res = lookup_addr(127.0.0.1) )
+		{
+		return;
+		}
+
 	print "done";
 }