diff --git a/R/checks.R b/R/checks.R
index e8b5970..5f6f5c5 100644
--- a/R/checks.R
+++ b/R/checks.R
@@ -17,23 +17,24 @@ kernel_type <- function(kern) {
 process_options <- function(M, se.method, method, d, kern) {
     if (kernel_type(kern)=="optimal" && method!="SRD")
         stop("Optimal kernel requires sharp RD design.")
+    m_len <- if (method=="FRD") 2 else 1
     if (!missing(M)) {
-        m_len <- if (method=="FRD") 2 else 1
         if (!check_positive(M, m_len))
             stop(paste0("M must be a non-negative numeric vector of length",
                         m_len, "."))
     }
 
-    if (min(sum(d$p), sum(d$m))==0) {
+    if (method=="IP") {
+        if (!is.null(d$covs))
+            stop("Covariates not allowed whem method is 'IP'.")
+    } else if (min(sum(d$p), sum(d$m))==0) {
         stop("No observations on one side of the cutoff")
     }
+
     if (!(se.method %in% c("nn", "EHW", "supplied.var"))) {
         stop("Unsupported se.method")
     }
     if (se.method=="nn" && !is.null(d$clusterid))
         stop(paste0("'se.method=\"nn\"' not allowed with clustered standard",
                     "  errors.\nUse 'se.method=\"EHW\"'"))
-
-    if (!is.null(d$covs) && method=="IP")
-        stop("Covariates not allowed whem method is 'IP'.")
 }
diff --git a/doc/manual.pdf b/doc/manual.pdf
index 02bea79..31cc9a0 100644
Binary files a/doc/manual.pdf and b/doc/manual.pdf differ
diff --git a/tests/testthat/test_interface.R b/tests/testthat/test_interface.R
index e745471..667230f 100644
--- a/tests/testthat/test_interface.R
+++ b/tests/testthat/test_interface.R
@@ -4,10 +4,8 @@ test_that("Test inputs", {
     expect_error(r2 <- RDHonest(log(cn)~elig_year, data=rcp, kern="Unif"))
     expect_error(RDHonest(log(cn)|retired~elig_year, data=rcp, M=1, T0=0,
                           kern="optimal"))
-    expect_message(pp <- RDHonest(voteshare~margin, data=lee08,
-                                  M=2, h=5, subset=I(margin>0))$coefficients)
-    expect_equal(as.numeric(pp[c(2, 3, 11)]),
-                 c(0L, sqrt(.Machine$double.xmax/10), NA))
+    expect_error(pp <- RDHonest(voteshare~margin, data=lee08,
+                                M=2, h=5, subset=I(margin>0))$coefficients)
     expect_error(RDHonest(c~elig_year, data=rcp, clusterid=seq_along(rr$c),
                           point.inference=TRUE))
     ## Insufficient unique values of the running variable to compute rule of