diff --git a/laymanshex.go b/laymanshex.go
index 8bc77d4..c5d4db1 100644
--- a/laymanshex.go
+++ b/laymanshex.go
@@ -310,7 +310,7 @@ func setValues(descr fileDescription, binpath string, vals map[string]string) {
 	f, err := os.OpenFile(binpath, os.O_RDWR, 0666)
 	optPanic("failed to write-open binary", err)
 	defer f.Close()
-	for _, part := range descr.parts {
+	for i, part := range descr.parts {
 		needSeek := true
 		if part.name != "" {
 			if val, ok := vals[part.name]; ok {
@@ -319,7 +319,8 @@ func setValues(descr fileDescription, binpath string, vals map[string]string) {
 			}
 		}
 		if needSeek {
-			f.Seek(part.handling.bytes, 1)
+			_, err = f.Seek(part.handling.bytes, 1)
+			optPanic("set: could not advance in file (stuck at part "+strconv.Itoa(i)+"name: "+part.name+")", err)
 		}
 	}
 }
@@ -329,9 +330,10 @@ func getValues(descr fileDescription, binpath string) map[string]string {
 	f, err := os.Open(binpath)
 	defer f.Close()
 	optPanic("failed to open binary", err)
-	for _, part := range descr.parts {
+	for i, part := range descr.parts {
 		if part.name == "" {
-			f.Seek(part.handling.bytes, 1)
+			_, err = f.Seek(part.handling.bytes, 1)
+			optPanic("get: could not advance in file (stuck at part "+strconv.Itoa(i)+"name: "+part.name+")", err)
 		} else {
 			vals[part.name] = part.handling.readFrom(f, descr.byteOrder)
 		}