diff --git a/src/chunk.c b/src/chunk.c
index b600aba0..9a7bd45e 100644
--- a/src/chunk.c
+++ b/src/chunk.c
@@ -539,13 +539,21 @@ chunk_boot(void)
 	SYSTEM_INFO info;
 	GetSystemInfo(&info);
 
-	/* Verify actual page size is equal to or an integral multiple of configured page size */
+	/*
+	 * Verify actual page size is equal to or an integral multiple of
+	 * configured page size.
+	 */
 	if (info.dwPageSize & ((1U << LG_PAGE) - 1))
 		return (true);
 
-	/* Configure chunksize (if not set) to match granularity (usually 64K), so pages_map will always take fast path */
-	if (!opt_lg_chunk)
-		opt_lg_chunk = ffs((int)info.dwAllocationGranularity) - 1;
+	/*
+	 * Configure chunksize (if not set) to match granularity (usually 64K),
+	 * so pages_map will always take fast path.
+	 */
+	if (!opt_lg_chunk) {
+		opt_lg_chunk = jemalloc_ffs((int)info.dwAllocationGranularity)
+		    - 1;
+	}
 #else
 	if (!opt_lg_chunk)
 		opt_lg_chunk = LG_CHUNK_DEFAULT;