diff --git a/backend/src/api/fee-api.ts b/backend/src/api/fee-api.ts
index 8293520bf..2ad9744d2 100644
--- a/backend/src/api/fee-api.ts
+++ b/backend/src/api/fee-api.ts
@@ -18,9 +18,9 @@ class FeeApi {
       };
     }
 
-    const firstMedianFee = this.optimizeMedianFee(pBlocks[0]);
-    const secondMedianFee = pBlocks[1] ? this.optimizeMedianFee(pBlocks[1], firstMedianFee) : this.defaultFee;
-    const thirdMedianFee = pBlocks[2] ? this.optimizeMedianFee(pBlocks[2], secondMedianFee) : this.defaultFee;
+    const firstMedianFee = this.optimizeMedianFee(pBlocks[0], pBlocks[1]);
+    const secondMedianFee = pBlocks[1] ? this.optimizeMedianFee(pBlocks[1], pBlocks[2], firstMedianFee) : this.defaultFee;
+    const thirdMedianFee = pBlocks[2] ? this.optimizeMedianFee(pBlocks[2], pBlocks[3], secondMedianFee) : this.defaultFee;
 
     return {
       'fastestFee': firstMedianFee,
@@ -29,12 +29,12 @@ class FeeApi {
     };
   }
 
-  private optimizeMedianFee(pBlock: MempoolBlock, previousFee?: number): number {
+  private optimizeMedianFee(pBlock: MempoolBlock, nextBlock: MempoolBlock | undefined, previousFee?: number): number {
     const useFee = previousFee ? (pBlock.medianFee + previousFee) / 2 : pBlock.medianFee;
     if (pBlock.blockVSize <= 500000) {
       return this.defaultFee;
     }
-    if (pBlock.blockVSize <= 950000) {
+    if (pBlock.blockVSize <= 950000 && nextBlock) {
       const multiplier = (pBlock.blockVSize - 500000) / 500000;
       return Math.max(Math.round(useFee * multiplier), this.defaultFee);
     }
diff --git a/frontend/src/app/components/fees-box/fees-box.component.ts b/frontend/src/app/components/fees-box/fees-box.component.ts
index d52916127..8823891f7 100644
--- a/frontend/src/app/components/fees-box/fees-box.component.ts
+++ b/frontend/src/app/components/fees-box/fees-box.component.ts
@@ -40,9 +40,9 @@ export class FeesBoxComponent implements OnInit {
             };
           }
 
-          const firstMedianFee = this.optimizeMedianFee(pBlocks[0]);
-          const secondMedianFee = pBlocks[1] ? this.optimizeMedianFee(pBlocks[1], firstMedianFee) : this.defaultFee;
-          const thirdMedianFee = pBlocks[2] ? this.optimizeMedianFee(pBlocks[2], secondMedianFee) : this.defaultFee;
+          const firstMedianFee = this.optimizeMedianFee(pBlocks[0], pBlocks[1]);
+          const secondMedianFee = pBlocks[1] ? this.optimizeMedianFee(pBlocks[1], pBlocks[2], firstMedianFee) : this.defaultFee;
+          const thirdMedianFee = pBlocks[2] ? this.optimizeMedianFee(pBlocks[2], pBlocks[3], secondMedianFee) : this.defaultFee;
 
           return {
             'fastestFee': firstMedianFee,
@@ -53,12 +53,12 @@ export class FeesBoxComponent implements OnInit {
       );
   }
 
-  optimizeMedianFee(pBlock: MempoolBlock, previousFee?: number): number {
+  private optimizeMedianFee(pBlock: MempoolBlock, nextBlock: MempoolBlock | undefined, previousFee?: number): number {
     const useFee = previousFee ? (pBlock.medianFee + previousFee) / 2 : pBlock.medianFee;
     if (pBlock.blockVSize <= 500000) {
       return this.defaultFee;
     }
-    if (pBlock.blockVSize <= 950000) {
+    if (pBlock.blockVSize <= 950000 && nextBlock) {
       const multiplier = (pBlock.blockVSize - 500000) / 500000;
       return Math.max(Math.round(useFee * multiplier), this.defaultFee);
     }