diff --git a/packages/verified-fetch/src/utils/byte-range-context.ts b/packages/verified-fetch/src/utils/byte-range-context.ts
index 1979ad1..fe8f4a2 100644
--- a/packages/verified-fetch/src/utils/byte-range-context.ts
+++ b/packages/verified-fetch/src/utils/byte-range-context.ts
@@ -42,7 +42,13 @@ function getByteRangeFromHeader (rangeHeader: string): { start: string, end: str
 
 export class ByteRangeContext {
   private readonly _isRangeRequest: boolean
-  private _fileSize: number | null | undefined
+
+  /**
+   * This property should only be set by calling `setFileSize` or `setBody`.
+   *
+   * @access private
+   */
+  public fileSize: Readonly<number | null | undefined>
   private readonly _contentRangeHeaderValue: string | undefined
   private _body: SupportedBodyTypes | null = null
   private readonly _rangeRequestHeader: string | undefined
@@ -80,12 +86,15 @@ export class ByteRangeContext {
     }
   }
 
+  /**
+   * When you get a body, it should be set here, and we will calculate the fileSize if possible.
+   */
   public setBody (body: SupportedBodyTypes): void {
     this._body = body
     // if fileSize was already set, don't recalculate it
-    this.fileSize = this.fileSize ?? getBodySizeSync(body)
+    this.setFileSize(this.fileSize ?? getBodySizeSync(body))
 
-    this.log.trace('set request body with fileSize %o', this._fileSize)
+    this.log.trace('set request body with fileSize %o', this.fileSize)
   }
 
   public getBody (): SupportedBodyTypes {
@@ -139,18 +148,20 @@ export class ByteRangeContext {
     return this.requestRangeStart != null && this.requestRangeEnd == null
   }
 
-  // sometimes, we need to set the fileSize explicitly because we can't calculate the size of the body (e.g. for unixfs content where we call .stat)
-  public set fileSize (size: number | bigint | null) {
-    this._fileSize = size != null ? Number(size) : null
-    this.log.trace('set _fileSize to %o', this._fileSize)
+  /**
+   * Sometimes, we need to set the fileSize explicitly because we can't calculate
+   * the size of the body (e.g. for unixfs content where we call .stat).
+   *
+   * This fileSize should otherwise only be called from `setBody`, and `.fileSize`
+   * should not be set directly.
+   */
+  public setFileSize (size: number | bigint | null): void {
+    this.fileSize = size != null ? Number(size) : null
+    this.log.trace('set _fileSize to %o', this.fileSize)
     // when fileSize changes, we need to recalculate the offset details
     this.setOffsetDetails()
   }
 
-  public get fileSize (): number | null | undefined {
-    return this._fileSize
-  }
-
   public get isRangeRequest (): boolean {
     return this._isRangeRequest
   }
@@ -259,7 +270,7 @@ export class ByteRangeContext {
       return
     }
 
-    const { start, end, byteSize } = calculateByteRangeIndexes(this.requestRangeStart ?? undefined, this.requestRangeEnd ?? undefined, this._fileSize ?? undefined)
+    const { start, end, byteSize } = calculateByteRangeIndexes(this.requestRangeStart ?? undefined, this.requestRangeEnd ?? undefined, this.fileSize ?? undefined)
     this.log.trace('set byteStart to %o, byteEnd to %o, byteSize to %o', start, end, byteSize)
     this.byteStart = start
     this.byteEnd = end
@@ -290,7 +301,7 @@ export class ByteRangeContext {
     return getContentRangeHeader({
       byteStart: this.byteStart,
       byteEnd: this.byteEnd,
-      byteSize: this._fileSize ?? undefined
+      byteSize: this.fileSize ?? undefined
     })
   }
 }
diff --git a/packages/verified-fetch/src/verified-fetch.ts b/packages/verified-fetch/src/verified-fetch.ts
index c6161dd..4c75180 100644
--- a/packages/verified-fetch/src/verified-fetch.ts
+++ b/packages/verified-fetch/src/verified-fetch.ts
@@ -334,7 +334,7 @@ export class VerifiedFetch {
 
     // we have to .stat before .cat so we can get the size and make sure byte offsets are calculated properly
     if (byteRangeContext.isRangeRequest && byteRangeContext.isValidRangeRequest && terminalElement.type === 'file') {
-      byteRangeContext.fileSize = terminalElement.unixfs.fileSize()
+      byteRangeContext.setFileSize(terminalElement.unixfs.fileSize())
 
       this.log.trace('fileSize for rangeRequest %d', byteRangeContext.fileSize)
     }
diff --git a/packages/verified-fetch/test/utils/byte-range-context.spec.ts b/packages/verified-fetch/test/utils/byte-range-context.spec.ts
index e70fa79..abf7ef9 100644
--- a/packages/verified-fetch/test/utils/byte-range-context.spec.ts
+++ b/packages/verified-fetch/test/utils/byte-range-context.spec.ts
@@ -126,7 +126,7 @@ describe('ByteRangeContext', () => {
           leafType: 'file'
         })
         const stat = await fs.stat(cid)
-        context.fileSize = stat.fileSize
+        context.setFileSize(stat.fileSize)
 
         context.setBody(await getBodyStream(context.offset, context.length))
         const response = new Response(context.getBody())