diff --git a/lib/libkvm/kvm.c b/lib/libkvm/kvm.c
index d8862c1137b3..a4818b6fce87 100644
--- a/lib/libkvm/kvm.c
+++ b/lib/libkvm/kvm.c
@@ -375,12 +375,12 @@ kvm_read(kd, kva, buf, len)
 		errno = 0;
 		if (lseek(kd->vmfd, (off_t)kva, 0) == -1 && errno != 0) {
 			_kvm_err(kd, 0, "invalid address (%x)", kva);
-			return (0);
+			return (-1);
 		}
 		cc = read(kd->vmfd, buf, len);
 		if (cc < 0) {
 			_kvm_syserr(kd, 0, "kvm_read");
-			return (0);
+			return (-1);
 		} else if (cc < len)
 			_kvm_err(kd, kd->program, "short read");
 		return (cc);
@@ -391,7 +391,7 @@ kvm_read(kd, kva, buf, len)
 
 			cc = _kvm_kvatop(kd, kva, &pa);
 			if (cc == 0)
-				return (0);
+				return (-1);
 			if (cc > len)
 				cc = len;
 			errno = 0;
@@ -437,19 +437,19 @@ kvm_write(kd, kva, buf, len)
 		errno = 0;
 		if (lseek(kd->vmfd, (off_t)kva, 0) == -1 && errno != 0) {
 			_kvm_err(kd, 0, "invalid address (%x)", kva);
-			return (0);
+			return (-1);
 		}
 		cc = write(kd->vmfd, buf, len);
 		if (cc < 0) {
 			_kvm_syserr(kd, 0, "kvm_write");
-			return (0);
+			return (-1);
 		} else if (cc < len)
 			_kvm_err(kd, kd->program, "short write");
 		return (cc);
 	} else {
 		_kvm_err(kd, kd->program,
 		    "kvm_write not implemented for dead kernels");
-		return (0);
+		return (-1);
 	}
 	/* NOTREACHED */
 }