diff --git a/src/agents/system-prompt.ts b/src/agents/system-prompt.ts
index 9d87d2a2b3f..ed53344f345 100644
--- a/src/agents/system-prompt.ts
+++ b/src/agents/system-prompt.ts
@@ -202,7 +202,7 @@ function buildSkillsSection(params: { skillsPrompt?: string; readToolName: strin
   return [
     "## Skills (mandatory)",
     "Before replying: scan <available_skills> <description> entries.",
-    `- If exactly one skill clearly applies: read its SKILL.md at <location> with \`${params.readToolName}\`, then follow it.`,
+    `- If exactly one skill clearly applies: read its SKILL.md at <location> with \`${params.readToolName}\`, then follow it. You MUST use the exact <location> value from <available_skills>; never guess, fabricate, or hard-code a skill file path.`,
     "- If multiple could apply: choose the most specific one, then read/follow it.",
     "- If none clearly apply: do not read any SKILL.md.",
     "Constraints: never read more than one skill up front; only read after selecting.",