diff --git a/R/expandMagclass.R b/R/expandMagclass.R
new file mode 100644
index 00000000..a0cc766e
--- /dev/null
+++ b/R/expandMagclass.R
@@ -0,0 +1,11 @@
+expandMagclass <- function(x, ref, fill = 0) {
+  r <- new.magpie(
+    cells_and_regions = union(getRegions(x), getRegions(ref)),
+    years = union(getYears(x), getYears(ref)),
+    names = union(getNames(x), getNames(ref)),
+    fill = fill,
+    sets = names(dimnames(ref))
+  )
+  r[getRegions(x), getYears(x), getNames(x)] <- x
+  return(r)
+}
diff --git a/tests/testthat/test-expandMagclass.R b/tests/testthat/test-expandMagclass.R
new file mode 100644
index 00000000..28b6f971
--- /dev/null
+++ b/tests/testthat/test-expandMagclass.R
@@ -0,0 +1,38 @@
+test_that("expandMagclass works", {
+  region <- c("AAA", "BBB", "CCC")
+  t <- paste0("y", c(2000, 2005, 2010))
+  name <- c("foo", "bar", "bazz")
+
+  A <- new.magpie(
+    cells_and_regions = region, years = t, names = name, fill = 1,
+    sets = c("region", "t", "name")
+  )
+
+  # spatial ----
+
+  ## x smaller than ref ----
+  B <- expandMagclass(A[region[-2], , ], A)
+  expect_true(all(region %in% getRegions(B)))
+
+  ## x larger than ref ----
+  expect_equal(expandMagclass(A, A[region[-2], , ]), A)
+
+  # temporal ----
+
+  ## x smaller than ref ----
+  B <- expandMagclass(A[, t[-2], ], A)
+  expect_true(all(t %in% getYears(B)))
+
+  ## x larger than ref ----
+  expect_equal(expandMagclass(x = A, ref = A[, t[-2], ]), A)
+
+  # names ----
+
+  ## x smaller than ref ----
+  B <- expandMagclass(A[,,name[-2]], A)
+  expect_true(all(name %in% getNames(B)))
+
+  ## x larger than ref ----
+  expect_equal(expandMagclass(A, A[,,name[-2]]), A)
+
+})