diff --git a/R/era.R b/R/era.R
index 95c6aeb..de4a63c 100644
--- a/R/era.R
+++ b/R/era.R
@@ -161,7 +161,8 @@ validate_era <- function(x) {
   # scale
   # direction
   if (!era_direction(x) %in% c(-1, 1)) {
-    stop("direction must be -1 (backwards) or 1 (forwards)")
+   abort("`direction` must be -1 (backwards) or 1 (forwards)",
+         class = "era_invalid_era")
   }
 }
 
diff --git a/R/transform.R b/R/transform.R
index 4a82322..537e6c6 100644
--- a/R/transform.R
+++ b/R/transform.R
@@ -40,8 +40,14 @@ yr_transform <- function(x, era = yr_era(x)) {
 
   # Check comparable units
   if (era_unit(src_era) != era_unit(dst_era)) {
-    stop("No method for transforming ", era_unit(src_era), " to ",
-         era_unit(dst_era), " years")
+    abort(
+      paste0("Can't transform era ", era_label(src_era), " to ", era_label(dst_era), ":"),
+      class = "era_invalid_transform",
+      body = format_error_bullets(c(
+        x = paste0("Can't convert ", era_unit(src_era), " to ",
+                   era_unit(dst_era), " years.")
+        ))
+      )
   }
 
   # Rescale to 1 (if not already)
diff --git a/R/yr.R b/R/yr.R
index acd60b5..68ce225 100644
--- a/R/yr.R
+++ b/R/yr.R
@@ -37,7 +37,8 @@ yr <- function(x = numeric(), era) {
   x <- vec_cast(x, numeric())
 
   if (vec_size(era) > 1) {
-    stop("yr vectors can only have one era attribute")
+    abort("yr vectors must have only one `era` attribute.",
+          class = "era_invalid_yr")
   }
   if (is.character(era)) {
     era <- era(era)
diff --git a/tests/testthat/test-transform.R b/tests/testthat/test-transform.R
index c016cb8..4b7d3f7 100644
--- a/tests/testthat/test-transform.R
+++ b/tests/testthat/test-transform.R
@@ -1,4 +1,4 @@
 test_that("yr_transform() throws an error for different units", {
   expect_error(yr_transform(yr(9000, "bp"), era("BP")),
-               "No method for transforming radiocarbon to calendar years")
+               class = "era_invalid_transform")
 })
diff --git a/tests/testthat/test-yr.R b/tests/testthat/test-yr.R
index f477a37..25fc40e 100644
--- a/tests/testthat/test-yr.R
+++ b/tests/testthat/test-yr.R
@@ -5,8 +5,7 @@ test_that("yr() constructs an era_yr with valid input", {
 })
 
 test_that("yr() throws an error with multiple eras", {
-  expect_error(yr(1, era(c("BC", "BP"))),
-               "yr vectors can only have one era attribute")
+  expect_error(yr(1, era(c("BC", "BP"))), class = "era_invalid_yr")
 })
 
 test_that("format.yr returns correct output", {