diff --git a/.changeset/block-personal-workspace-merge.md b/.changeset/block-personal-workspace-merge.md
new file mode 100644
index 0000000000..a845151cc8
--- /dev/null
+++ b/.changeset/block-personal-workspace-merge.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/server/src/db/org-merge-db.ts b/server/src/db/org-merge-db.ts
index 93d9737385..4d891d8377 100644
--- a/server/src/db/org-merge-db.ts
+++ b/server/src/db/org-merge-db.ts
@@ -68,7 +68,7 @@ export async function mergeOrganizations(
 
     // Validate both organizations exist and fetch all needed fields
     const orgsResult = await client.query(
-      `SELECT workos_organization_id, name, prospect_notes,
+      `SELECT workos_organization_id, name, is_personal, prospect_notes,
               enrichment_at, enrichment_industry, enrichment_sub_industry,
               enrichment_employee_count, enrichment_revenue, enrichment_revenue_range,
               enrichment_country, enrichment_city, enrichment_description
@@ -88,6 +88,11 @@ export async function mergeOrganizations(
       throw new Error('Could not load organization details');
     }
 
+    // Block merging personal workspaces
+    if (primaryOrg.is_personal || secondaryOrg.is_personal) {
+      throw new Error('Cannot merge personal workspaces. Personal workspaces represent individual users and should not be merged with company organizations.');
+    }
+
     logger.info(
       { primary: primaryOrg.name, secondary: secondaryOrg.name },
       'Merging organizations'
@@ -662,9 +667,9 @@ export async function previewMerge(
 }> {
   const pool = getPool();
 
-  // Get organization names
+  // Get organization names and personal workspace status
   const orgsResult = await pool.query(
-    `SELECT workos_organization_id, name FROM organizations
+    `SELECT workos_organization_id, name, is_personal FROM organizations
      WHERE workos_organization_id = ANY($1)`,
     [[primaryOrgId, secondaryOrgId]]
   );
@@ -681,6 +686,14 @@ export async function previewMerge(
   }
 
   const warnings: string[] = [];
+
+  // Warn if either organization is a personal workspace
+  if (primaryOrg.is_personal) {
+    warnings.unshift(`🔴 PRIMARY IS PERSONAL WORKSPACE: "${primaryOrg.name}" is a personal workspace and should not be merged with company organizations.`);
+  }
+  if (secondaryOrg.is_personal) {
+    warnings.unshift(`🔴 SECONDARY IS PERSONAL WORKSPACE: "${secondaryOrg.name}" is a personal workspace and should not be merged with company organizations.`);
+  }
   const estimatedChanges: { table_name: string; rows_to_move: number }[] = [];
 
   // Count rows in each table
diff --git a/server/src/routes/admin/cleanup.ts b/server/src/routes/admin/cleanup.ts
index f81028d453..24afee2c36 100644
--- a/server/src/routes/admin/cleanup.ts
+++ b/server/src/routes/admin/cleanup.ts
@@ -307,6 +307,15 @@ export function setupCleanupRoutes(apiRouter: Router): void {
       res.json(result);
     } catch (error) {
       logger.error({ err: error }, "Error executing merge");
+
+      // Return 400 for validation errors (e.g., personal workspace merge attempts)
+      if (error instanceof Error && error.message.startsWith('Cannot merge personal workspaces')) {
+        return res.status(400).json({
+          error: "Validation error",
+          message: error.message,
+        });
+      }
+
       res.status(500).json({
         error: "Internal server error",
         message: