diff --git a/config/trading.ts b/config/trading.ts
index dd76693..51e847a 100644
--- a/config/trading.ts
+++ b/config/trading.ts
@@ -271,7 +271,16 @@ export function calculateActualPositionSize(
   }
   
   // Percentage of free collateral
-  const percentDecimal = configuredSize / 100
+  let percentDecimal = configuredSize / 100
+  
+  // CRITICAL: Safety buffer for 100% positions
+  // Drift's margin calculation includes fees and buffer, so 100% exact causes InsufficientCollateral
+  // Use 99% when user configures 100% to leave room for fees/slippage
+  if (configuredSize >= 100) {
+    percentDecimal = 0.99
+    console.log(`⚠️ Applying 99% safety buffer for 100% position (prevents InsufficientCollateral from fees/slippage)`)
+  }
+  
   const calculatedSize = freeCollateral * percentDecimal
   
   console.log(`📊 Percentage sizing: ${configuredSize}% of $${freeCollateral.toFixed(2)} = $${calculatedSize.toFixed(2)}`)