diff --git a/lib/output.js b/lib/output.js
index ae0b1036fcb..46e1e656e9d 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -259,7 +259,9 @@ function OutputStream(options) {
         if (line_fixed || flush) flush_mappings();
     } : noop;
 
-    var require_semicolon = makePredicate("( [ + * / - , .");
+    var stat_end_chars = makePredicate("; }");
+    var asi_skip_chars = makePredicate("( [ + * / - , . `");
+    var asi_skip_words = makePredicate("in instanceof");
 
     function require_space(prev, ch, str) {
         return is_identifier_char(prev) && (is_identifier_char(ch) || ch == "\\")
@@ -295,8 +297,8 @@ function OutputStream(options) {
         var prev = last.slice(-1);
         if (might_need_semicolon) {
             might_need_semicolon = false;
-            if (prev == ":" && ch == "}" || prev != ";" && (!ch || ";}".indexOf(ch) < 0)) {
-                var need_semicolon = require_semicolon[ch];
+            if (prev != ";" && !stat_end_chars[ch]) {
+                var need_semicolon = asi_skip_chars[ch] || asi_skip_words[str];
                 if (need_semicolon || options.semicolons) {
                     output += ";";
                     current_col++;
@@ -941,7 +943,12 @@ function OutputStream(options) {
     DEFPRINT(AST_LabeledStatement, function(output) {
         this.label.print(output);
         output.colon();
-        this.body.print(output);
+        var body = this.body;
+        if (body instanceof AST_EmptyStatement) {
+            output.force_semicolon();
+        } else {
+            body.print(output);
+        }
     });
     DEFPRINT(AST_SimpleStatement, function(output) {
         this.body.print(output);
diff --git a/test/compress/classes.js b/test/compress/classes.js
index 4335809bb63..c1d7fdde361 100644
--- a/test/compress/classes.js
+++ b/test/compress/classes.js
@@ -4112,3 +4112,68 @@ issue_5876_2: {
     ]
     node_version: ">=12"
 }
+
+issue_5878_1: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        new class {
+            p = {};
+            in = console.log("PASS");
+        }();
+    }
+    expect_exact: 'new class{p={};in=console.log("PASS")}\n'
+    expect_stdout: "PASS"
+    node_version: ">=12"
+}
+
+issue_5878_2: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        class A {
+            static p = console.log("PASS");
+            instanceof() {}
+        }
+    }
+    expect_exact: 'class A{static p=console.log("PASS");instanceof(){}}'
+    expect_stdout: "PASS"
+    node_version: ">=12"
+}
+
+issue_5878_3: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        new class {
+            p;
+            in = console.log("PASS");
+        }();
+    }
+    expect_exact: 'new class{p;in=console.log("PASS")}\n'
+    expect_stdout: "PASS"
+    node_version: ">=12"
+}
+
+issue_5878_4: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        "use strict";
+        console.log(typeof class {
+            f() {}
+            instanceof() {}
+        });
+    }
+    expect_exact: [
+        '"use strict"',
+        "console.log(typeof class{f(){}instanceof(){}})",
+        "",
+    ]
+    expect_stdout: "function"
+    node_version: ">=4"
+}
diff --git a/test/compress/labels.js b/test/compress/labels.js
index c455f3d1de1..5d7d2e60620 100644
--- a/test/compress/labels.js
+++ b/test/compress/labels.js
@@ -431,3 +431,41 @@ issue_5524: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5878_1: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        console.log("PASS");
+        L:;
+    }
+    expect_exact: 'console.log("PASS")\nL:;'
+    expect_stdout: "PASS"
+}
+
+issue_5878_2: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        L: ;
+        L: console.log("PASS");
+    }
+    expect_exact: 'L:;L:console.log("PASS")\n'
+    expect_stdout: "PASS"
+}
+
+issue_5878_3: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        if (console.log("PASS"))
+            A:;
+        else
+            B:;
+    }
+    expect_exact: 'if(console.log("PASS"))A:;else B:;'
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/regexp.js b/test/compress/regexp.js
index 3324a0c8e35..05630243ed0 100644
--- a/test/compress/regexp.js
+++ b/test/compress/regexp.js
@@ -489,3 +489,15 @@ reset_state_between_evaluate: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5878: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        console.log("PASS");
+        /b/.exec({});
+    }
+    expect_exact: 'console.log("PASS");/b/.exec({})\n'
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/templates.js b/test/compress/templates.js
index db3ab203c96..4658f0d8828 100644
--- a/test/compress/templates.js
+++ b/test/compress/templates.js
@@ -769,3 +769,16 @@ issue_5199: {
     expect_stdout: "undefined"
     node_version: ">=4"
 }
+
+issue_5878: {
+    beautify = {
+        semicolons: false,
+    }
+    input: {
+        console.log("PASS");
+        `42`;
+    }
+    expect_exact: 'console.log("PASS");`42`\n'
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
diff --git a/test/sandbox.js b/test/sandbox.js
index 71d1e09fff3..a4d799809aa 100644
--- a/test/sandbox.js
+++ b/test/sandbox.js
@@ -65,7 +65,7 @@ exports.patch_module_statements = function(code, module) {
         return "";
     }).replace(/\bexport(?:\s*\{[^{}]*}\s*?(?:$|\n|;)|\s+default\b(?:\s*(\(|\{|class\s*\{|class\s+(?=extends\b)|(?:async\s+)?function\s*(?:\*\s*)?\())?|\b)/g, function(match, header) {
         if (/^export\s+default/.test(match)) has_default = "function _uglify_export_default_() {}";
-        if (!header) return "";
+        if (!header) return ";";
         if (header.length == 1) return "0, " + header;
         var name = "_uglify_export_default_";
         if (/^class\b/.test(header)) do {
@@ -85,7 +85,7 @@ exports.patch_module_statements = function(code, module) {
                 "} = new Proxy(Object.create(null), { get(_, value) { return { value }; } });",
             ].join(""));
         }
-        return "";
+        return ";";
     });
     imports.push("");
     return strict_mode + has_default + imports.join("\n") + code;
diff --git a/test/ufuzz/index.js b/test/ufuzz/index.js
index eb38de375cd..15adc00d71e 100644
--- a/test/ufuzz/index.js
+++ b/test/ufuzz/index.js
@@ -2173,7 +2173,8 @@ function log_suspects(minify_options, component) {
     var defs = default_options[component];
     var toplevel = sandbox.has_toplevel(minify_options);
     var suspects = Object.keys(defs).filter(function(name) {
-        var flip = component == "compress" && name == "keep_fargs";
+        var flip = component == "compress" && name == "keep_fargs"
+            || component == "output" && name == "semicolons";
         if (flip !== (name in options ? options : defs)[name]) {
             var m = JSON.parse(JSON.stringify(minify_options));
             var o = JSON.parse(JSON.stringify(options));
diff --git a/test/ufuzz/options.json b/test/ufuzz/options.json
index ef479f73c8b..9fad3d5e88a 100644
--- a/test/ufuzz/options.json
+++ b/test/ufuzz/options.json
@@ -23,6 +23,9 @@
     {
         "ie": true,
         "module": false,
+        "output": {
+            "semicolons": false
+        },
         "toplevel": true
     },
     {