diff --git a/.changeset/lively-moles-caper.md b/.changeset/lively-moles-caper.md
new file mode 100644
index 000000000..a24af0393
--- /dev/null
+++ b/.changeset/lively-moles-caper.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 3043
+---
+milestone complete now scopes phase stats to the explicit version argument and errors when that version is missing from a versioned ROADMAP milestone section.
diff --git a/get-shit-done/bin/lib/core.cjs b/get-shit-done/bin/lib/core.cjs
index a51b80f09..43cefdeaa 100644
--- a/get-shit-done/bin/lib/core.cjs
+++ b/get-shit-done/bin/lib/core.cjs
@@ -1895,10 +1895,62 @@ function getMilestoneInfo(cwd) {
  * to the current milestone based on ROADMAP.md phase headings.
  * If no ROADMAP exists or no phases are listed, returns a pass-all filter.
  */
-function getMilestonePhaseFilter(cwd) {
+function getMilestonePhaseFilter(cwd, versionOverride) {
   const milestonePhaseNums = new Set();
+  let missingExplicitVersion = false;
   try {
-    const roadmap = extractCurrentMilestone(fs.readFileSync(path.join(planningDir(cwd), 'ROADMAP.md'), 'utf-8'), cwd);
+    const roadmapPath = path.join(planningDir(cwd), 'ROADMAP.md');
+    const roadmapContent = fs.readFileSync(roadmapPath, 'utf-8');
+    let roadmap = extractCurrentMilestone(roadmapContent, cwd);
+
+    if (versionOverride) {
+      const escapedVersion = escapeRegex(versionOverride);
+      const sectionPattern = new RegExp(`(^#{1,3}\\s+.*${escapedVersion}[^\\n]*)`, 'mi');
+      const sectionMatch = roadmapContent.match(sectionPattern);
+      if (!sectionMatch) {
+        // Only treat this as an error case when the roadmap is milestone-versioned.
+        // Older/flat roadmap formats without vX.Y milestone headings should keep
+        // legacy pass-through behavior for milestone.complete.
+        const hasVersionedMilestones = /^#{1,3}\s+.*v\d+\.\d+/mi.test(roadmapContent);
+        if (hasVersionedMilestones) {
+          roadmap = '';
+          missingExplicitVersion = true;
+        }
+      } else {
+        const sectionStart = sectionMatch.index;
+        const headingLevel = sectionMatch[1].match(/^(#{1,3})\s/)[1].length;
+        const restContent = roadmapContent.slice(sectionStart + sectionMatch[0].length);
+        const nextMilestonePattern = new RegExp(`^#{1,${headingLevel}}\\s+(?!Phase\\s+\\S)(?:.*v\\d+\\.\\d+|✅|📋|🚧)`, 'i');
+
+        let sectionEnd = roadmapContent.length;
+        let fenceChar = null;
+        let fenceLen = 0;
+        let charOffset = 0;
+        for (const line of restContent.split('\n')) {
+          const fenceMatch = line.match(/^\s{0,3}((?:`{3,}|~{3,}))(.*)/);
+          if (fenceMatch) {
+            const char = fenceMatch[1][0];
+            const len = fenceMatch[1].length;
+            const trailing = fenceMatch[2] || '';
+            if (!fenceChar) {
+              fenceChar = char;
+              fenceLen = len;
+            } else if (char === fenceChar && len >= fenceLen && /^\s*$/.test(trailing)) {
+              fenceChar = null;
+              fenceLen = 0;
+            }
+          } else if (!fenceChar && nextMilestonePattern.test(line)) {
+            sectionEnd = sectionStart + sectionMatch[0].length + charOffset;
+            break;
+          }
+          charOffset += line.length + 1;
+        }
+
+        const currentSection = roadmapContent.slice(sectionStart, sectionEnd);
+        roadmap = currentSection;
+      }
+    }
+
     // Match both numeric phases (Phase 1:) and custom IDs (Phase PROJ-42:)
     const phasePattern = /#{2,4}\s*Phase\s+([\w][\w.-]*)\s*:/gi;
     let m;
@@ -1910,6 +1962,7 @@ function getMilestonePhaseFilter(cwd) {
   if (milestonePhaseNums.size === 0) {
     const passAll = () => true;
     passAll.phaseCount = 0;
+    passAll.missingExplicitVersion = missingExplicitVersion;
     return passAll;
   }
 
@@ -1927,6 +1980,7 @@ function getMilestonePhaseFilter(cwd) {
     return false;
   }
   isDirInMilestone.phaseCount = milestonePhaseNums.size;
+  isDirInMilestone.missingExplicitVersion = missingExplicitVersion;
   return isDirInMilestone;
 }
 
diff --git a/get-shit-done/bin/lib/milestone.cjs b/get-shit-done/bin/lib/milestone.cjs
index 23c8dd4ba..d891ee362 100644
--- a/get-shit-done/bin/lib/milestone.cjs
+++ b/get-shit-done/bin/lib/milestone.cjs
@@ -107,7 +107,10 @@ function cmdMilestoneComplete(cwd, version, options, raw) {
   // Scope stats and accomplishments to only the phases belonging to the
   // current milestone's ROADMAP.  Uses the shared filter from core.cjs
   // (same logic used by cmdPhasesList and other callers).
-  const isDirInMilestone = getMilestonePhaseFilter(cwd);
+  const isDirInMilestone = getMilestonePhaseFilter(cwd, version);
+  if (isDirInMilestone.missingExplicitVersion) {
+    error(`no phases found for milestone ${version} in ROADMAP.md`);
+  }
 
   // Gather stats from phases (scoped to current milestone only)
   let phaseCount = 0;
diff --git a/tests/bug-3043-milestone-complete-scope.test.cjs b/tests/bug-3043-milestone-complete-scope.test.cjs
new file mode 100644
index 000000000..2235aba14
--- /dev/null
+++ b/tests/bug-3043-milestone-complete-scope.test.cjs
@@ -0,0 +1,57 @@
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+const { createTempProject, cleanup, runGsdTools } = require('./helpers.cjs');
+
+describe('bug #3043: milestone complete respects explicit version scope', () => {
+  test('milestone.complete v3.6 uses v3.6 phases even when STATE milestone is v3.5', () => {
+    const tmpDir = createTempProject('gsd-bug-3043-');
+    try {
+      fs.writeFileSync(path.join(tmpDir, '.planning', 'STATE.md'), '---\nmilestone: v3.5\n---\n');
+      fs.writeFileSync(
+        path.join(tmpDir, '.planning', 'ROADMAP.md'),
+        '# Roadmap\n\n## 🚧 v3.5 Paused\n### Phase 103: old\n### Phase 104: old2\n\n## 🚧 v3.6 Current\n### Phase 108: new\n',
+      );
+      fs.writeFileSync(path.join(tmpDir, '.planning', 'REQUIREMENTS.md'), '# Requirements\n');
+
+      const oldDirA = path.join(tmpDir, '.planning', 'phases', '103.old');
+      const oldDirB = path.join(tmpDir, '.planning', 'phases', '104.old');
+      const newDir = path.join(tmpDir, '.planning', 'phases', '108.new');
+      fs.mkdirSync(oldDirA, { recursive: true });
+      fs.mkdirSync(oldDirB, { recursive: true });
+      fs.mkdirSync(newDir, { recursive: true });
+      fs.writeFileSync(path.join(oldDirA, 'SUMMARY.md'), 'one-liner: old milestone A\n\n## Summary\nold\n');
+      fs.writeFileSync(path.join(oldDirB, 'SUMMARY.md'), 'one-liner: old milestone B\n\n## Summary\nold\n');
+      fs.writeFileSync(path.join(newDir, 'SUMMARY.md'), 'one-liner: new milestone\n\n## Summary\nnew\n');
+
+      const result = runGsdTools(['milestone', 'complete', 'v3.6', '--raw'], tmpDir);
+      assert.equal(result.success, true, result.error || result.output);
+      const payload = JSON.parse(result.output);
+
+      assert.equal(payload.version, 'v3.6');
+      assert.equal(payload.phases, 1, `expected v3.6 to scope to one phase, got ${payload.phases}`);
+    } finally {
+      cleanup(tmpDir);
+    }
+  });
+
+  test('milestone.complete fails when explicit milestone version resolves no phases', () => {
+    const tmpDir = createTempProject('gsd-bug-3043-empty-');
+    try {
+      fs.writeFileSync(path.join(tmpDir, '.planning', 'STATE.md'), '---\nmilestone: v1.0\n---\n');
+      fs.writeFileSync(
+        path.join(tmpDir, '.planning', 'ROADMAP.md'),
+        '# Roadmap\n\n## 🚧 v1.0\n### Phase 1: foundation\n',
+      );
+      fs.writeFileSync(path.join(tmpDir, '.planning', 'REQUIREMENTS.md'), '# Requirements\n');
+      fs.mkdirSync(path.join(tmpDir, '.planning', 'phases', '01-foundation'), { recursive: true });
+
+      const result = runGsdTools(['milestone', 'complete', 'v9.9', '--raw'], tmpDir);
+      assert.equal(result.success, false, 'expected command to fail when no phases match explicit version');
+      assert.match(result.error || '', /no phases|phase/i);
+    } finally {
+      cleanup(tmpDir);
+    }
+  });
+});