diff --git a/sys/dev/usb/usb_busdma.h b/sys/dev/usb/usb_busdma.h
--- a/sys/dev/usb/usb_busdma.h
+++ b/sys/dev/usb/usb_busdma.h
@@ -101,6 +101,7 @@
 					 * from the memory. Else write. */
 	uint8_t	ismultiseg:1;		/* set if we can have multiple
 					 * segments */
+	uint8_t isloaded:1;		/* Set if map is currently loaded. */
 #endif
 };
 
diff --git a/sys/dev/usb/usb_busdma.c b/sys/dev/usb/usb_busdma.c
--- a/sys/dev/usb/usb_busdma.c
+++ b/sys/dev/usb/usb_busdma.c
@@ -600,6 +600,7 @@
 		bus_dmamem_free(utag->tag, ptr, map);
 		goto error;
 	}
+	pc->isloaded = 1;
 	memset(ptr, 0, size);
 
 	usb_pc_cpu_flush(pc);
@@ -612,6 +613,7 @@
 	pc->page_start = NULL;
 	pc->page_offset_buf = 0;
 	pc->page_offset_end = 0;
+	pc->isloaded = 0;
 	pc->map = NULL;
 	pc->tag = NULL;
 	return (1);
@@ -626,11 +628,13 @@
 usb_pc_free_mem(struct usb_page_cache *pc)
 {
 	if (pc && pc->buffer) {
-		bus_dmamap_unload(pc->tag, pc->map);
+		if (pc->isloaded)
+			bus_dmamap_unload(pc->tag, pc->map);
 
 		bus_dmamem_free(pc->tag, pc->buffer, pc->map);
 
 		pc->buffer = NULL;
+		pc->isloaded = 0;
 	}
 }
 
@@ -662,7 +666,8 @@
 			 * We have to unload the previous loaded DMA
 			 * pages before trying to load a new one!
 			 */
-			bus_dmamap_unload(pc->tag, pc->map);
+			if (pc->isloaded)
+				bus_dmamap_unload(pc->tag, pc->map);
 
 			/*
 			 * Try to load memory into DMA.
@@ -675,6 +680,7 @@
 				err = 0;
 			}
 			if (err || uptag->dma_error) {
+				pc->isloaded = 0;
 				return (1);
 			}
 		} else {
@@ -682,7 +688,8 @@
 			 * We have to unload the previous loaded DMA
 			 * pages before trying to load a new one!
 			 */
-			bus_dmamap_unload(pc->tag, pc->map);
+			if (pc->isloaded)
+				bus_dmamap_unload(pc->tag, pc->map);
 
 			/*
 			 * Try to load memory into DMA. The callback
@@ -693,6 +700,7 @@
 			    &usb_pc_load_mem_cb, pc, BUS_DMA_WAITOK)) {
 			}
 		}
+		pc->isloaded = 1;
 	} else {
 		if (!sync) {
 			/*
@@ -785,6 +793,8 @@
 usb_pc_dmamap_destroy(struct usb_page_cache *pc)
 {
 	if (pc && pc->tag) {
+		if (pc->isloaded)
+			bus_dmamap_unload(pc->tag, pc->map);
 		bus_dmamap_destroy(pc->tag, pc->map);
 		pc->tag = NULL;
 		pc->map = NULL;