diff --git a/packages/kboot/src/util/usb/encode-command-option.ts b/packages/kboot/src/util/usb/encode-command-option.ts
index 621269fa375..5f08c97e6b1 100644
--- a/packages/kboot/src/util/usb/encode-command-option.ts
+++ b/packages/kboot/src/util/usb/encode-command-option.ts
@@ -26,7 +26,7 @@ export const encodeCommandOption = (option: CommandOption): number[] => {
     ];
 
     const placeholders = new Array(32 - payload.length)
-        .fill(0);
+        .fill(0) as number[];
 
     return [...header, ...payload, ...placeholders];
 };
diff --git a/packages/mcumgr/src/serial-peripheral.ts b/packages/mcumgr/src/serial-peripheral.ts
index 9d30d35df7f..d6685942f59 100644
--- a/packages/mcumgr/src/serial-peripheral.ts
+++ b/packages/mcumgr/src/serial-peripheral.ts
@@ -79,7 +79,7 @@ export class SerialPeripheral implements Peripheral {
         const startTime = new Date().getTime();
 
         while (true) {
-            const response = this.#serialPort.read();
+            const response = this.#serialPort.read() as Buffer;
             logger('Read response: %o', response);
             let exit = false;
 
diff --git a/packages/mcumgr/src/util/cbor.ts b/packages/mcumgr/src/util/cbor.ts
index a3d84c68529..de281ebd357 100644
--- a/packages/mcumgr/src/util/cbor.ts
+++ b/packages/mcumgr/src/util/cbor.ts
@@ -289,7 +289,7 @@ export function decode(data: ArrayBuffer | SharedArrayBuffer, tagger?: Function,
         }
     }
 
-    function decodeItem() {
+    function decodeItem(): unknown {
         const initialByte = readUint8();
         const majorType = initialByte >> 5;
         const additionalInformation = initialByte & 0x1f;
@@ -366,7 +366,7 @@ export function decode(data: ArrayBuffer | SharedArrayBuffer, tagger?: Function,
             case 5: {
                 const retObject = {};
                 for (i = 0; i < length || length < 0 && !readBreak(); ++i) {
-                    const key = decodeItem();
+                    const key = decodeItem() as string | number;
                     retObject[key] = decodeItem();
                 }
                 return retObject;