diff --git a/src/Stmt.cc b/src/Stmt.cc
index e8c4abc9f9..47e839e189 100644
--- a/src/Stmt.cc
+++ b/src/Stmt.cc
@@ -1570,10 +1570,10 @@ TraversalCode NullStmt::Traverse(TraversalCallback* cb) const {
     HANDLE_TC_STMT_POST(tc);
 }
 
-AssertStmt::AssertStmt(ExprPtr arg_cond, ExprPtr arg_msg)
-    : Stmt(STMT_ASSERT), cond(std::move(arg_cond)), msg(std::move(arg_msg)) {
-    if ( ! IsBool(cond->GetType()->Tag()) )
-        cond->Error("conditional must be boolean");
+AssertStmt::AssertStmt(ExprPtr cond, ExprPtr arg_msg)
+    : ExprStmt(STMT_ASSERT, std::move(cond)), msg(std::move(arg_msg)) {
+    if ( ! IsBool(e->GetType()->Tag()) )
+        e->Error("conditional must be boolean");
 
     if ( msg && ! IsString(msg->GetType()->Tag()) )
         msg->Error("message must be string");
@@ -1581,7 +1581,7 @@ AssertStmt::AssertStmt(ExprPtr arg_cond, ExprPtr arg_msg)
     zeek::ODesc desc;
     desc.SetShort(true);
     desc.SetQuotes(true);
-    cond->Describe(&desc);
+    e->Describe(&desc);
 
     cond_desc = desc.Description();
 }
@@ -1592,7 +1592,7 @@ ValPtr AssertStmt::Exec(Frame* f, StmtFlowType& flow) {
 
     static auto assertion_result_hook = id::find_func("assertion_result");
     bool run_result_hook = assertion_result_hook && assertion_result_hook->HasEnabledBodies();
-    auto assert_result = cond->Eval(f)->AsBool();
+    auto assert_result = e->Eval(f)->AsBool();
 
     if ( ! assert_result || run_result_hook ) {
         zeek::StringValPtr msg_val = zeek::val_mgr->EmptyString();
@@ -1619,7 +1619,13 @@ void AssertStmt::StmtDescribe(ODesc* d) const {
     auto orig_quotes = d->WantQuotes();
     d->SetQuotes(true);
 
-    cond->Describe(d);
+    e->Describe(d);
+
+    if ( msg_setup_stmt ) {
+        d->Add("{ ");
+        msg_setup_stmt->Describe(d);
+        d->Add(" }");
+    }
 
     if ( msg ) {
         d->Add(",");
@@ -1636,9 +1642,14 @@ TraversalCode AssertStmt::Traverse(TraversalCallback* cb) const {
     TraversalCode tc = cb->PreStmt(this);
     HANDLE_TC_STMT_PRE(tc);
 
-    tc = cond->Traverse(cb);
+    tc = e->Traverse(cb);
     HANDLE_TC_STMT_PRE(tc);
     if ( msg ) {
+        if ( msg_setup_stmt ) {
+            tc = msg_setup_stmt->Traverse(cb);
+            HANDLE_TC_STMT_PRE(tc);
+        }
+
         tc = msg->Traverse(cb);
         HANDLE_TC_STMT_PRE(tc);
     }
diff --git a/src/Stmt.h b/src/Stmt.h
index d714a61d56..9fac25752e 100644
--- a/src/Stmt.h
+++ b/src/Stmt.h
@@ -495,15 +495,15 @@ private:
     bool is_directive;
 };
 
-class AssertStmt final : public Stmt {
+class AssertStmt final : public ExprStmt {
 public:
     explicit AssertStmt(ExprPtr cond, ExprPtr msg = nullptr);
 
     ValPtr Exec(Frame* f, StmtFlowType& flow) override;
 
-    const auto& Cond() const { return cond; }
     const auto& CondDesc() const { return cond_desc; }
     const auto& Msg() const { return msg; }
+    const auto& MsgSetupStmt() const { return msg_setup_stmt; }
 
     void StmtDescribe(ODesc* d) const override;
 
@@ -516,9 +516,12 @@ public:
     StmtPtr DoReduce(Reducer* c) override;
 
 private:
-    ExprPtr cond;
     std::string cond_desc;
     ExprPtr msg;
+
+    // Statement to execute before evaluating "msg". Only used for script
+    // optimization.
+    StmtPtr msg_setup_stmt;
 };
 
 // Helper function for reporting on asserts that either failed, or should
diff --git a/src/script_opt/CPP/Stmts.cc b/src/script_opt/CPP/Stmts.cc
index fadb8e989a..ace13e4e24 100644
--- a/src/script_opt/CPP/Stmts.cc
+++ b/src/script_opt/CPP/Stmts.cc
@@ -480,7 +480,7 @@ void CPPCompile::GenForOverString(const ExprPtr& str, const IDPList* loop_vars)
 }
 
 void CPPCompile::GenAssertStmt(const AssertStmt* a) {
-    auto& cond = a->Cond();
+    auto cond = a->StmtExpr();
     auto& msg = a->Msg();
 
     Emit("{ // begin a new scope for internal \"assert\" variables");
diff --git a/src/script_opt/Stmt.cc b/src/script_opt/Stmt.cc
index 8ef72c60b4..8c1f7d4bf0 100644
--- a/src/script_opt/Stmt.cc
+++ b/src/script_opt/Stmt.cc
@@ -1070,11 +1070,36 @@ StmtPtr InitStmt::DoReduce(Reducer* c) {
     return ThisPtr();
 }
 
-StmtPtr AssertStmt::Duplicate() { return SetSucc(new AssertStmt(cond->Duplicate(), msg ? msg->Duplicate() : nullptr)); }
+StmtPtr AssertStmt::Duplicate() { return SetSucc(new AssertStmt(e->Duplicate(), msg ? msg->Duplicate() : nullptr)); }
 
-bool AssertStmt::IsReduced(Reducer* c) const { return false; }
+bool AssertStmt::IsReduced(Reducer* c) const {
+    if ( ! analysis_options.keep_asserts )
+        return false;
 
-StmtPtr AssertStmt::DoReduce(Reducer* c) { return TransformMe(make_intrusive<NullStmt>(), c); }
+    return e->IsSingleton(c) && (! msg || msg->IsSingleton(c));
+}
+
+StmtPtr AssertStmt::DoReduce(Reducer* c) {
+    if ( ! analysis_options.keep_asserts )
+        return TransformMe(make_intrusive<NullStmt>(), c);
+
+    if ( c->Optimizing() ) {
+        e = c->OptExpr(e);
+        if ( msg )
+            msg = c->OptExpr(msg);
+        return ThisPtr();
+    }
+    else if ( IsReduced(c) )
+        return ThisPtr();
+
+    StmtPtr red_stmt;
+    e = e->ReduceToSingleton(c, red_stmt);
+    if ( msg )
+        msg = msg->ReduceToSingleton(c, msg_setup_stmt);
+
+    auto sl = with_location_of(make_intrusive<StmtList>(red_stmt, ThisPtr()), this);
+    return sl->Reduce(c);
+}
 
 bool WhenInfo::HasUnreducedIDs(Reducer* c) const {
     for ( auto& cp : *cl ) {
diff --git a/src/script_opt/UseDefs.cc b/src/script_opt/UseDefs.cc
index e0edc9a85b..ad238e6dcb 100644
--- a/src/script_opt/UseDefs.cc
+++ b/src/script_opt/UseDefs.cc
@@ -287,6 +287,21 @@ UDs UseDefs::PropagateUDs(const Stmt* s, UDs succ_UDs, const Stmt* succ_stmt, bo
             return CreateUDs(s, uds);
         }
 
+        case STMT_ASSERT: {
+            auto a = s->AsAssertStmt();
+            auto e = a->StmtExpr();
+
+            if ( auto msg = a->Msg().get() ) {
+                succ_UDs = UD_Union(succ_UDs, ExprUDs(msg));
+                if ( auto msg_setup_stmt = a->MsgSetupStmt().get() ) {
+                    succ_UDs = PropagateUDs(msg_setup_stmt, succ_UDs, succ_stmt, second_pass);
+                    succ_stmt = msg_setup_stmt;
+                }
+            }
+
+            return CreateUDs(s, UD_Union(succ_UDs, ExprUDs(e)));
+        }
+
         case STMT_SWITCH: {
             auto sw_UDs = std::make_shared<UseDefSet>();
 
diff --git a/src/script_opt/ZAM/Stmt.cc b/src/script_opt/ZAM/Stmt.cc
index 65a9d94e13..75075dfa86 100644
--- a/src/script_opt/ZAM/Stmt.cc
+++ b/src/script_opt/ZAM/Stmt.cc
@@ -48,6 +48,8 @@ const ZAMStmt ZAMCompiler::CompileStmt(const Stmt* s) {
 
         case STMT_WHEN: return CompileWhen(static_cast<const WhenStmt*>(s));
 
+        case STMT_ASSERT: return CompileAssert(static_cast<const AssertStmt*>(s));
+
         case STMT_NULL: return EmptyStmt();
 
         case STMT_CHECK_ANY_LEN: {
@@ -1047,6 +1049,45 @@ const ZAMStmt ZAMCompiler::CompileWhen(const WhenStmt* ws) {
     return AddInst(z);
 }
 
+const ZAMStmt ZAMCompiler::CompileAssert(const AssertStmt* as) {
+    auto cond = as->StmtExpr();
+
+    int cond_slot;
+    if ( cond->Tag() == EXPR_CONST )
+        cond_slot = TempForConst(cond->AsConstExpr());
+    else
+        cond_slot = FrameSlot(cond->AsNameExpr());
+
+    auto decision_slot = NewSlot(false);
+
+    (void)AddInst(ZInstI(OP_SHOULD_REPORT_ASSERT_VV, decision_slot, cond_slot));
+
+    ZInstI z;
+
+    // We don't have a convenient way of directly introducing a std::string
+    // constant, so we build one to hold it.
+    auto cond_desc = make_intrusive<StringVal>(new String(as->CondDesc()));
+    auto cond_desc_e = make_intrusive<ConstExpr>(cond_desc);
+
+    if ( auto msg = as->Msg() ) {
+        auto& msg_setup_stmt = as->MsgSetupStmt();
+        if ( msg_setup_stmt )
+            (void)CompileStmt(msg_setup_stmt);
+
+        int msg_slot;
+        if ( msg->Tag() == EXPR_CONST )
+            msg_slot = TempForConst(msg->AsConstExpr());
+        else
+            msg_slot = FrameSlot(msg->AsNameExpr());
+
+        z = ZInstI(OP_REPORT_ASSERT_WITH_MESSAGE_VVVC, decision_slot, cond_slot, msg_slot, cond_desc_e.get());
+    }
+    else
+        z = ZInstI(OP_REPORT_ASSERT_VVC, decision_slot, cond_slot, cond_desc_e.get());
+
+    return AddInst(z);
+}
+
 const ZAMStmt ZAMCompiler::InitRecord(IDPtr id, RecordType* rt) {
     auto z = ZInstI(OP_INIT_RECORD_V, FrameSlot(id));
     z.SetType({NewRef{}, rt});
diff --git a/src/script_opt/ZAM/Stmt.h b/src/script_opt/ZAM/Stmt.h
index 8a85ed4539..242fbe8197 100644
--- a/src/script_opt/ZAM/Stmt.h
+++ b/src/script_opt/ZAM/Stmt.h
@@ -20,6 +20,7 @@ const ZAMStmt CompileCatchReturn(const CatchReturnStmt* cr);
 const ZAMStmt CompileStmts(const StmtList* sl);
 const ZAMStmt CompileInit(const InitStmt* is);
 const ZAMStmt CompileWhen(const WhenStmt* ws);
+const ZAMStmt CompileAssert(const AssertStmt* ws);
 
 const ZAMStmt CompileNext() { return GenGoTo(nexts.back()); }
 const ZAMStmt CompileBreak() { return GenGoTo(breaks.back()); }
diff --git a/src/script_opt/ZAM/Vars.h b/src/script_opt/ZAM/Vars.h
index 5fe46e9fe4..affc88ec69 100644
--- a/src/script_opt/ZAM/Vars.h
+++ b/src/script_opt/ZAM/Vars.h
@@ -25,8 +25,8 @@ int FrameSlotIfName(const Expr* e) {
     return n ? FrameSlot(n->Id()) : -1;
 }
 
-int FrameSlot(const NameExpr* id) { return FrameSlot(id->AsNameExpr()->Id()); }
-int Frame1Slot(const NameExpr* id, ZOp op) { return Frame1Slot(id->AsNameExpr()->Id(), op); }
+int FrameSlot(const NameExpr* n) { return FrameSlot(n->Id()); }
+int Frame1Slot(const NameExpr* n, ZOp op) { return Frame1Slot(n->Id(), op); }
 
 int Frame1Slot(const ID* id, ZOp op) { return Frame1Slot(id, op1_flavor[op]); }
 int Frame1Slot(const NameExpr* n, ZAMOp1Flavor fl) { return Frame1Slot(n->Id(), fl); }