diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 81f020fe6535..dcce241104ed 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -100,6 +100,7 @@ static struct io_tlb_mem io_tlb_default_mem;
 
 static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
 static unsigned long default_nareas;
+static bool swiotlb_cmdline_size_set __initdata;
 
 /**
  * struct io_tlb_area - IO TLB memory area descriptor
@@ -253,6 +254,7 @@ setup_io_tlb_npages(char *str)
 		/* avoid tail segment of size < IO_TLB_SEGSIZE */
 		default_nslabs =
 			ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE);
+		swiotlb_cmdline_size_set = true;
 	}
 	if (*str == ',')
 		++str;
@@ -295,7 +297,7 @@ void __init swiotlb_adjust_size(unsigned long size)
 	 * architectures such as those supporting memory encryption to
 	 * adjust/expand SWIOTLB size for their use.
 	 */
-	if (default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT)
+	if (swiotlb_cmdline_size_set)
 		return;
 
 	default_nslabs = swiotlb_calc_nslabs(size, default_nareas);