diff --git a/autoload/ale/lsp/response.vim b/autoload/ale/lsp/response.vim
index 48740ad1..b389ab18 100644
--- a/autoload/ale/lsp/response.vim
+++ b/autoload/ale/lsp/response.vim
@@ -47,7 +47,12 @@ function! ale#lsp#response#ReadDiagnostics(response) abort
         endif
 
         if has_key(l:diagnostic, 'code')
-            let l:loclist_item.nr = l:diagnostic.code
+            if type(l:diagnostic.code) == v:t_string
+                let l:loclist_item.code = l:diagnostic.code
+            elseif type(l:diagnostic.code) == v:t_number && l:diagnostic.code != -1
+                let l:loclist_item.code = string(l:diagnostic.code)
+                let l:loclist_item.nr = l:diagnostic.code
+            endif
         endif
 
         call add(l:loclist, l:loclist_item)
@@ -70,7 +75,12 @@ function! ale#lsp#response#ReadTSServerDiagnostics(response) abort
         \}
 
         if has_key(l:diagnostic, 'code')
-            let l:loclist_item.nr = l:diagnostic.code
+            if type(l:diagnostic.code) == v:t_string
+                let l:loclist_item.code = l:diagnostic.code
+            elseif type(l:diagnostic.code) == v:t_number && l:diagnostic.code != -1
+                let l:loclist_item.code = string(l:diagnostic.code)
+                let l:loclist_item.nr = l:diagnostic.code
+            endif
         endif
 
         if get(l:diagnostic, 'category') is# 'warning'
diff --git a/doc/ale.txt b/doc/ale.txt
index 15a20469..e68ba9df 100644
--- a/doc/ale.txt
+++ b/doc/ale.txt
@@ -2318,6 +2318,12 @@ ale#linter#Define(filetype, linter)                       *ale#linter#Define()*
                          `type` - Defaults to `'E'`.
                          `nr` - Defaults to `-1`.
 
+                           Numeric error code. If `nr` is not `-1`, `code` should have
+                           the same value.
+                         `code` - No default.
+
+                           String error code.
+
   `executable`             A |String| naming the executable itself which
                          will be run. This value will be used to check if the
                          program requested is installed or not.
diff --git a/test/lsp/test_read_lsp_diagnostics.vader b/test/lsp/test_read_lsp_diagnostics.vader
index 444272aa..134a7161 100644
--- a/test/lsp/test_read_lsp_diagnostics.vader
+++ b/test/lsp/test_read_lsp_diagnostics.vader
@@ -18,7 +18,7 @@ Execute(ale#lsp#response#ReadDiagnostics() should handle errors):
   \     'col': 11,
   \     'end_lnum': 5,
   \     'end_col': 16,
-  \     'nr': 'some-error',
+  \     'code': 'some-error',
   \   }
   \ ],
   \ ale#lsp#response#ReadDiagnostics({'params': {'uri': 'filename.ts', 'diagnostics': [
@@ -39,7 +39,7 @@ Execute(ale#lsp#response#ReadDiagnostics() should handle warnings):
   \     'col': 4,
   \     'end_lnum': 2,
   \     'end_col': 4,
-  \     'nr': 'some-warning',
+  \     'code': 'some-warning',
   \   }
   \ ],
   \ ale#lsp#response#ReadDiagnostics({'params': {'uri': 'filename.ts', 'diagnostics': [
@@ -60,7 +60,7 @@ Execute(ale#lsp#response#ReadDiagnostics() should treat messages with missing se
   \     'col': 11,
   \     'end_lnum': 5,
   \     'end_col': 16,
-  \     'nr': 'some-error',
+  \     'code': 'some-error',
   \   }
   \ ],
   \ ale#lsp#response#ReadDiagnostics({'params': {'uri': 'filename.ts', 'diagnostics': [
@@ -126,6 +126,7 @@ Execute(ale#lsp#response#ReadTSServerDiagnostics() should handle tsserver respon
   \   {
   \     'type': 'E',
   \     'nr': 2365,
+  \     'code': '2365',
   \     'text': 'Operator ''''+'''' cannot be applied to types ''''3'''' and ''''{}''''.',
   \     'lnum': 1,
   \     'col': 11,
@@ -142,6 +143,7 @@ Execute(ale#lsp#response#ReadTSServerDiagnostics() should handle warnings from t
   \     'lnum': 27,
   \     'col': 3,
   \     'nr': 2515,
+  \     'code': '2515',
   \     'end_lnum': 27,
   \     'type': 'W',
   \     'end_col': 14,
@@ -157,6 +159,7 @@ Execute(ale#lsp#response#ReadTSServerDiagnostics() should handle suggestions fro
   \     'lnum': 27,
   \     'col': 3,
   \     'nr': 2515,
+  \     'code': '2515',
   \     'end_lnum': 27,
   \     'type': 'I',
   \     'end_col': 14,
diff --git a/test/test_engine_lsp_response_handling.vader b/test/test_engine_lsp_response_handling.vader
index 517d82c0..ddcd7b2e 100644
--- a/test/test_engine_lsp_response_handling.vader
+++ b/test/test_engine_lsp_response_handling.vader
@@ -62,6 +62,7 @@ Execute(tsserver syntax error responses should be handled correctly):
   \     'col': 14,
   \     'vcol': 0,
   \     'nr': 1005,
+  \     'code': '1005',
   \     'type': 'E',
   \     'text': ''','' expected.',
   \     'valid': 1,
@@ -135,6 +136,7 @@ Execute(tsserver semantic error responses should be handled correctly):
   \     'col': 14,
   \     'vcol': 0,
   \     'nr': 1005,
+  \     'code': '1005',
   \     'type': 'E',
   \     'text': 'Some semantic error',
   \     'valid': 1,
diff --git a/test/test_ignoring_linters.vader b/test/test_ignoring_linters.vader
index af31fce3..1ddd30e8 100644
--- a/test/test_ignoring_linters.vader
+++ b/test/test_ignoring_linters.vader
@@ -190,6 +190,7 @@ Execute(Buffer ignore lists should be applied for tsserver):
   \     'lnum': 2,
   \     'col': 14,
   \     'nr': 1005,
+  \     'code': '1005',
   \     'type': 'E',
   \     'end_col': 15,
   \     'end_lnum': 2,