diff --git a/internal/lsp/source/completion.go b/internal/lsp/source/completion.go
index 712b595ebe..3bf3fed756 100644
--- a/internal/lsp/source/completion.go
+++ b/internal/lsp/source/completion.go
@@ -1424,7 +1424,9 @@ Nodes:
 							// param w/ further expressions, we expect a single
 							// variadic item.
 							if beyondLastParam || isLastParam && len(node.Args) > numParams {
-								inf.objType = sig.Params().At(numParams - 1).Type().(*types.Slice).Elem()
+								if slice, ok := sig.Params().At(numParams - 1).Type().(*types.Slice); ok {
+									inf.objType = slice.Elem()
+								}
 								break Nodes
 							}
 
diff --git a/internal/lsp/testdata/lsp/primarymod/builtins/builtin_args.go b/internal/lsp/testdata/lsp/primarymod/builtins/builtin_args.go
index 0ce5aa4802..d115ada455 100644
--- a/internal/lsp/testdata/lsp/primarymod/builtins/builtin_args.go
+++ b/internal/lsp/testdata/lsp/primarymod/builtins/builtin_args.go
@@ -22,6 +22,8 @@ func _() {
 
 	append() //@rank(")", builtinSlice, builtinChan)
 
+	var _ []byte = append([]byte(nil), ""...) //@rank(") //")
+
 	copy()           //@rank(")", builtinSlice, builtinChan)
 	copy(aSlice, aS) //@rank(")", builtinSlice, builtinString)
 	copy(aS, aSlice) //@rank(",", builtinSlice, builtinString)
diff --git a/internal/lsp/testdata/lsp/summary.txt.golden b/internal/lsp/testdata/lsp/summary.txt.golden
index 739316e565..c5efd04365 100644
--- a/internal/lsp/testdata/lsp/summary.txt.golden
+++ b/internal/lsp/testdata/lsp/summary.txt.golden
@@ -4,7 +4,7 @@ CompletionSnippetCount = 67
 UnimportedCompletionsCount = 11
 DeepCompletionsCount = 5
 FuzzyCompletionsCount = 8
-RankedCompletionsCount = 85
+RankedCompletionsCount = 86
 CaseSensitiveCompletionsCount = 4
 DiagnosticsCount = 38
 FoldingRangesCount = 2