diff --git a/generator/gen_wrapper_util.js b/generator/gen_wrapper_util.js
index f1d75dfe..1f91f6b1 100644
--- a/generator/gen_wrapper_util.js
+++ b/generator/gen_wrapper_util.js
@@ -65,7 +65,28 @@ const decomposeWhenClause = function(when) {
         return result;
     };
     const tokens = when.split(/(\|\||\&\&)/);
-    const ors_of_ands = splitArray(tokens, '||').map(a =>
+    let nest = 0;
+    const outMostTokens = [];
+    for (let i = 0; i < tokens.length; i++) {
+        let str = tokens[i];
+        let open = 0, close = 0;
+        let m;
+        while ((m = str.match(/^\s*(\!\s*)*[(]/)) !== null) {
+            open += 1;
+            str = str.slice(m[0].length);
+        }
+        while ((m = str.match(/[)]\s*$/)) !== null) {
+            close += 1;
+            str = str.slice(0, str.length - m[0].length);
+        }
+        if (nest === 0) {
+            outMostTokens.push(tokens[i]);
+        } else {
+            outMostTokens[outMostTokens.length - 1] += tokens[i];
+        }
+        nest += open - close;
+    }
+    const ors_of_ands = splitArray(outMostTokens, '||').map(a =>
         splitArray(a, '&&').map(x => x.join('').trim())
     );
     return ors_of_ands;
diff --git a/test/suite/gen_wrapper_util.test.js b/test/suite/gen_wrapper_util.test.js
index 51a1bafe..cf555f14 100644
--- a/test/suite/gen_wrapper_util.test.js
+++ b/test/suite/gen_wrapper_util.test.js
@@ -23,15 +23,24 @@ describe('gen_wrapper_util', () => {
             assert.deepStrictEqual(decomposeWhenClause('!c'), [['!c']]);
             assert.deepStrictEqual(decomposeWhenClause('c1 || !c2 || !!c3'), [['c1'], ['!c2'], ['!!c3']]);
         });
-        // TODO: https://github.com/tshino/vscode-kb-macro/issues/296
-        /*
         it('should leave parenthesized portion unchanged', () => {
             assert.deepStrictEqual(decomposeWhenClause('(c1 || c2)'), [['(c1 || c2)']]);
             assert.deepStrictEqual(decomposeWhenClause('!(c1 || c2)'), [['!(c1 || c2)']]);
             assert.deepStrictEqual(decomposeWhenClause('c1 && (c2 || c3)'), [['c1', '(c2 || c3)']]);
             assert.deepStrictEqual(decomposeWhenClause('c1 || (c2 && c3)'), [['c1'], ['(c2 && c3)']]);
         });
-        */
+        it('should handle nested parenthesized portion', () => {
+            assert.deepStrictEqual(decomposeWhenClause('((c1 || c2))'), [['((c1 || c2))']]);
+            assert.deepStrictEqual(decomposeWhenClause('(!(c1 || c2))'), [['(!(c1 || c2))']]);
+            assert.deepStrictEqual(decomposeWhenClause('c1 && ((c2 && c3) || c4)'), [['c1', '((c2 && c3) || c4)']]);
+            assert.deepStrictEqual(decomposeWhenClause('(c1 || !(c2 && c3)) && c4'), [['(c1 || !(c2 && c3))', 'c4']]);
+        });
+        it('should handle spaces around parentheses', () => {
+            assert.deepStrictEqual(decomposeWhenClause('( (c1 || c2)) || c3'), [['( (c1 || c2))'], ['c3']]);
+            assert.deepStrictEqual(decomposeWhenClause('((c1 || c2) ) || c3'), [['((c1 || c2) )'], ['c3']]);
+            assert.deepStrictEqual(decomposeWhenClause('! (c1 || c2)'), [['! (c1 || c2)']]);
+            assert.deepStrictEqual(decomposeWhenClause('( !(c1 || c2))'), [['( !(c1 || c2))']]);
+        });
     });
     describe('addWhenContext', () => {
         const addWhenContext = genWrapperUtil.addWhenContext;