diff --git a/lib/compress.js b/lib/compress.js
index 211f6b2564..74e09299b2 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -646,14 +646,12 @@ Compressor.prototype.compress = function(node) {
             scope.may_call_this = undefined;
         }
 
-        function push(tw, sequential) {
+        function push(tw, sequential, conditional) {
             var defined_ids = Object.create(tw.defined_ids);
-            var safe_ids = Object.create(tw.safe_ids);
-            if (!sequential) {
-                defined_ids.seq = Object.create(null);
-                safe_ids.seq = {};
-            }
+            if (!sequential || conditional) defined_ids.seq = Object.create(null);
             tw.defined_ids = defined_ids;
+            var safe_ids = Object.create(tw.safe_ids);
+            if (!sequential) safe_ids.seq = {};
             tw.safe_ids = safe_ids;
         }
 
@@ -855,7 +853,7 @@ Compressor.prototype.compress = function(node) {
             var scanner = new TreeWalker(function(node) {
                 if (node instanceof AST_DefaultValue) {
                     reset_flags(node);
-                    push(tw, true);
+                    push(tw, true, true);
                     node.value.walk(tw);
                     pop(tw);
                     var save = fixed;
@@ -1042,7 +1040,7 @@ Compressor.prototype.compress = function(node) {
                     return walk_lazy();
                 }
                 var safe = safe_to_read(tw, ld);
-                if (lazy) push(tw, true);
+                if (lazy) push(tw, true, true);
                 right.walk(tw);
                 if (lazy) pop(tw);
                 if (safe && !left.in_arg && safe_to_assign(tw, ld)) {
@@ -1127,7 +1125,7 @@ Compressor.prototype.compress = function(node) {
             function walk_lazy() {
                 if (!lazy) return;
                 left.walk(tw);
-                push(tw, true);
+                push(tw, true, true);
                 right.walk(tw);
                 pop(tw);
                 return true;
@@ -1136,7 +1134,7 @@ Compressor.prototype.compress = function(node) {
         def(AST_Binary, function(tw) {
             if (!lazy_op[this.operator]) return;
             this.left.walk(tw);
-            push(tw, true);
+            push(tw, true, true);
             this.right.walk(tw);
             pop(tw);
             return true;
@@ -1166,7 +1164,7 @@ Compressor.prototype.compress = function(node) {
             }
             exp.walk(tw);
             var optional = node.optional;
-            if (optional) push(tw, true);
+            if (optional) push(tw, true, true);
             node.args.forEach(function(arg) {
                 arg.walk(tw);
             });
@@ -1251,16 +1249,16 @@ Compressor.prototype.compress = function(node) {
         });
         def(AST_Conditional, function(tw) {
             this.condition.walk(tw);
-            push(tw, true);
+            push(tw, true, true);
             this.consequent.walk(tw);
             pop(tw);
-            push(tw, true);
+            push(tw, true, true);
             this.alternative.walk(tw);
             pop(tw);
             return true;
         });
         def(AST_DefaultValue, function(tw) {
-            push(tw, true);
+            push(tw, true, true);
             this.value.walk(tw);
             pop(tw);
             this.name.walk(tw);
@@ -1349,11 +1347,11 @@ Compressor.prototype.compress = function(node) {
         });
         def(AST_If, function(tw) {
             this.condition.walk(tw);
-            push(tw, true);
+            push(tw, true, true);
             this.body.walk(tw);
             pop(tw);
             if (this.alternative) {
-                push(tw, true);
+                push(tw, true, true);
                 this.alternative.walk(tw);
                 pop(tw);
             }
@@ -1396,7 +1394,7 @@ Compressor.prototype.compress = function(node) {
             var expr = node.expression;
             if (node.optional) {
                 expr.walk(tw);
-                push(tw, true);
+                push(tw, true, true);
                 node.property.walk(tw);
                 pop(tw);
             } else {
@@ -1420,7 +1418,7 @@ Compressor.prototype.compress = function(node) {
                 branch.expression.walk(tw);
                 if (first) {
                     first = false;
-                    push(tw, true);
+                    push(tw, true, true);
                 }
             });
             if (!first) pop(tw);
@@ -1428,7 +1426,7 @@ Compressor.prototype.compress = function(node) {
             return true;
         });
         def(AST_SwitchBranch, function(tw) {
-            push(tw, true);
+            push(tw, true, true);
             walk_body(this, tw);
             pop(tw);
             return true;
@@ -1567,7 +1565,7 @@ Compressor.prototype.compress = function(node) {
             walk_body(node, tw);
             pop(tw);
             if (node.bcatch) {
-                push(tw, true);
+                push(tw, true, true);
                 node.bcatch.walk(tw);
                 pop(tw);
             }
diff --git a/test/compress/optional-chains.js b/test/compress/optional-chains.js
index a1594cf618..2a337e6c7e 100644
--- a/test/compress/optional-chains.js
+++ b/test/compress/optional-chains.js
@@ -693,3 +693,35 @@ issue_5905: {
     expect_stdout: "PASS"
     node_version: ">=14"
 }
+
+issue_5912: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a, b = {};
+        b = b.p;
+        a?.[b.q];
+        try {
+            b.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a, b = {};
+        b = b.p;
+        a?.[b.q];
+        try {
+            b.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=14"
+}
diff --git a/test/compress/side_effects.js b/test/compress/side_effects.js
index 9a7a4eb917..5ad46956ff 100644
--- a/test/compress/side_effects.js
+++ b/test/compress/side_effects.js
@@ -967,3 +967,104 @@ issue_5860_keep_3: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5912_1: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = {};
+        a = a.p;
+        console || a.q;
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = {};
+        a = a.p;
+        console || a.q;
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5912_2: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = {};
+        a = a.p;
+        if (!console) a.q;
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = {};
+        a = a.p;
+        if (!console) a.q;
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5912_3: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = {};
+        a = a.p;
+        try {
+            console;
+        } catch (e) {
+            a.q;
+        }
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = {};
+        a = a.p;
+        try {
+            console;
+        } catch (e) {
+            a.q;
+        }
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/switches.js b/test/compress/switches.js
index 681a919925..3c70fd0c62 100644
--- a/test/compress/switches.js
+++ b/test/compress/switches.js
@@ -1798,3 +1798,77 @@ issue_5892_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5912_1: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = {};
+        a = a.p;
+        switch (console) {
+          case 42:
+            a.q;
+        }
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = {};
+        a = a.p;
+        switch (console) {
+          case 42:
+            a.q;
+        }
+        try {
+            a.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5912_2: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a, b = {};
+        b = b.p;
+        switch (a) {
+          case void 0:
+          case b.q:
+        }
+        try {
+            b.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a, b = {};
+        b = b.p;
+        switch (a) {
+          case void 0:
+          case b.q:
+        }
+        try {
+            b.r;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}