diff --git a/src/lib/credentials.test.ts b/src/lib/credentials.test.ts
index fa7f744e..d6d27add 100644
--- a/src/lib/credentials.test.ts
+++ b/src/lib/credentials.test.ts
@@ -90,6 +90,30 @@ unknown_key = ignored
 `;
     expect(parseCredentials(content)).toEqual({ default: { apiKey: 'sk-real' } });
   });
+
+  it('reads a section header that carries a trailing comment', () => {
+    const content = `[default]
+api_key = sk-default
+[prod]  # production account
+api_key = sk-prod
+[dev] ; dev account
+api_key = sk-dev
+`;
+    expect(parseCredentials(content)).toEqual({
+      default: { apiKey: 'sk-default' },
+      prod: { apiKey: 'sk-prod' },
+      dev: { apiKey: 'sk-dev' },
+    });
+  });
+
+  it('never moves keys under an unreadable header into the section above it', () => {
+    const content = `[default]
+api_key = sk-default
+[prod] stray text
+api_key = sk-prod
+`;
+    expect(parseCredentials(content)).toEqual({ default: { apiKey: 'sk-default' } });
+  });
 });
 
 describe('serializeCredentials', () => {
diff --git a/src/lib/credentials.ts b/src/lib/credentials.ts
index b0eec1f0..3061bd79 100644
--- a/src/lib/credentials.ts
+++ b/src/lib/credentials.ts
@@ -136,7 +136,8 @@ export function parseCredentials(content: string): CredentialsFile {
   for (const rawLine of content.split('\n')) {
     const line = rawLine.trim();
     if (line === '' || line.startsWith('#') || line.startsWith(';')) continue;
-    const sectionMatch = /^\[([^\]]+)\]$/.exec(line);
+    // A header may carry a trailing comment (`[prod]  # production account`).
+    const sectionMatch = /^\[([^\]]+)\]\s*(?:[#;].*)?$/.exec(line);
     if (sectionMatch) {
       const sectionName = sectionMatch[1]!.trim();
       const existing = result[sectionName];
@@ -149,6 +150,13 @@ export function parseCredentials(content: string): CredentialsFile {
       }
       continue;
     }
+    // Any other `[`-line is a header we can't read. Its keys must not land in
+    // the section above it (that silently swapped one profile's key into
+    // another, and the next write lost the original key).
+    if (line.startsWith('[')) {
+      currentEntry = null;
+      continue;
+    }
     if (currentEntry === null) continue;
     const eqIndex = line.indexOf('=');
     if (eqIndex < 0) continue;