diff --git a/R/WeightedMean.R b/R/WeightedMean.R
index 81077ca4b92ddbf5b5cb5d1520cc12063da69cd1..393f56f680ffba9c459d69884043ed55f79a036b 100644
--- a/R/WeightedMean.R
+++ b/R/WeightedMean.R
@@ -124,11 +124,10 @@ WeightedMean <- function(data, lon, lat, region = NULL, mask = NULL, londim = NU
   cosphi <- t(array(cos(lat * pi / 180), dim = c(length(lat), length(lon))))
   nblat <- length(lat)
   nblon <- length(lon)
-  lon[lon > 180] = lon[lon > 180] - 360
-  dlon <- abs(c(abs(lon[2 : nblon]) - abs(lon[1 : nblon - 1]))) * pi / 180
+  dlon <- diff(lon) * pi / 180
   dlon <- c(dlon, dlon[1])
   dlon <- array(dlon, dim = c(nblon, nblat))
-  dlat <- abs(c(lat[2 : nblat] - lat[1 : nblat - 1])) * pi / 180
+  dlat <- diff(lat) * pi / 180
   dlat <- c(dlat, dlat[1])
   dlat <- t(array(dlat, dim = c(nblat, nblon)))
   weight <- (dlon * dlat * cosphi) 
diff --git a/tests/testthat/test-WeightedMean.R b/tests/testthat/test-WeightedMean.R
new file mode 100644
index 0000000000000000000000000000000000000000..2c5a23176bfe912072b9d12fbbdbafeb55615c5d
--- /dev/null
+++ b/tests/testthat/test-WeightedMean.R
@@ -0,0 +1,71 @@
+context("WeightedMean tests")
+set.seed(1)
+dat1 <- array(rnorm(10000), dim = c(lat = 50, lon = 100))
+lat1 <- seq(-90, 90, length.out = 50)
+lon1 <- seq(0, 360, length.out = 101)[1:100]
+
+set.seed(1)
+dat2 <- array(rnorm(10000), dim = c(lat = 180, lon = 360, sdate = 2))
+lat2 <- seq(-89.5, 89.5, length.out = 180)
+lon2 <- seq(-180, 179, length.out = 360)
+
+set.seed(1)
+dat3 <- array(rnorm(10000), dim = c(sdate = 2, lat = 171, lon = 350))
+lat3 <- seq(-90, 90, length.out = 181)[c(1:80, seq(81, 101, by = 2), 102:181)]
+lon3 <- seq(-180, 179, length.out = 360)[c(1:170, seq(171, 190, by = 2), 191:360)]
+
+set.seed(1)
+dat4 <- array(rnorm(10000), dim = c(lat = 180, lon = 360, sdate = 2, time = 1))
+lat4 <- seq(-89.5, 89.5, length.out = 180)
+lon4 <- seq(-179.5, 179.5, length.out = 360)
+
+
+test_that("dat1", {
+expect_equal(
+dim(WeightedMean(dat1, lat = lat1, lon = lon1)),
+NULL
+)
+expect_equal(
+as.vector(WeightedMean(dat1, lat = lat1, lon = lon1)),
+-0.009785971,
+tolerance = 0.0001
+)
+})
+
+test_that("dat2", {
+expect_equal(
+dim(WeightedMean(dat2, lat = lat2, lon = lon2)),
+NULL
+)
+expect_equal(
+as.vector(WeightedMean(dat2, lat = lat2, lon = lon2)),
+c(-0.005799676, -0.007599831),
+tolerance = 0.0001
+)
+})
+
+test_that("dat3", {
+expect_equal(
+dim(WeightedMean(dat3, lat = lat3, lon = lon3)),
+NULL
+)
+expect_equal(
+as.vector(WeightedMean(dat3, lat = lat3, lon = lon3)),
+c(-0.0253997, 0.0132251),
+tolerance = 0.0001
+)
+
+})
+
+
+test_that("dat4", {
+expect_equal(
+dim(WeightedMean(dat4, lat = lat4, lon = lon4)),
+c(sdate = 2, time = 1)
+)
+expect_equal(
+as.vector(WeightedMean(dat4, lat = lat4, lon = lon4)),
+c(-0.005799676, -0.007599831),
+tolerance = 0.0001
+)
+})