diff --git a/lib/steep/diagnostic/lsp_formatter.rb b/lib/steep/diagnostic/lsp_formatter.rb
index 0adf1a5c0..654c303a0 100644
--- a/lib/steep/diagnostic/lsp_formatter.rb
+++ b/lib/steep/diagnostic/lsp_formatter.rb
@@ -41,7 +41,7 @@ def format(diagnostic)
         severity = severity_for(diagnostic)
 
         if severity
-          range = diagnostic.location&.as_lsp_range or raise
+          range = diagnostic.location&.as_lsp_range or raise "#{diagnostic.class} object (#{diagnostic.full_message}) instance must have `#location`"
 
           LSP::Interface::Diagnostic.new(
             message: diagnostic.full_message,
diff --git a/lib/steep/diagnostic/ruby.rb b/lib/steep/diagnostic/ruby.rb
index 04a332686..bfa2896e5 100644
--- a/lib/steep/diagnostic/ruby.rb
+++ b/lib/steep/diagnostic/ruby.rb
@@ -286,13 +286,14 @@ class NoMethod < Base
         def initialize(node:, type:, method:)
           loc = case node.type
                 when :send
-                  node.loc.selector
+                  loc = _ = nil
+                  loc ||= node.loc.operator if node.loc.respond_to?(:operator)
+                  loc ||= node.loc.selector if node.loc.respond_to?(:selector)
+                  loc
                 when :block
                   node.children[0].loc.selector
-                else
-                  node.loc.expression
                 end
-          super(node: node, location: loc)
+          super(node: node, location: loc || node.loc.expression)
           @type = type
           @method = method
         end
diff --git a/test/type_construction_test.rb b/test/type_construction_test.rb
index bd7ffffaf..f63b36c13 100644
--- a/test/type_construction_test.rb
+++ b/test/type_construction_test.rb
@@ -10449,4 +10449,24 @@ def test_orasgn_andasgn__global
       end
     end
   end
+
+  def test_opasgn_error_report
+    with_checker(<<~RBS) do |checker|
+      RBS
+      source = parse_ruby(<<~RUBY)
+        x = [1].first
+
+        x += 1
+      RUBY
+
+      with_standard_construction(checker, source) do |construction, typing|
+        type, _, context = construction.synthesize(source.node)
+
+        assert_all!(typing.errors) do |error|
+          assert_operator error, :is_a?, Diagnostic::Ruby::NoMethod
+          assert_instance_of Parser::Source::Range, error.location
+        end
+      end
+    end
+  end
 end