diff --git a/src/Completion.cxx b/src/Completion.cxx
index 25102fa8..65c62c56 100644
--- a/src/Completion.cxx
+++ b/src/Completion.cxx
@@ -6,7 +6,7 @@
 #include <assert.h>
 
 Completion::Result
-Completion::Complete(const std::string &prefix) const noexcept
+Completion::Complete(const std::string_view prefix) const noexcept
 {
 	auto lower = list.lower_bound(prefix);
 	if (lower == list.end() || !lower->starts_with(prefix))
diff --git a/src/Completion.hxx b/src/Completion.hxx
index 47976812..73fb7059 100644
--- a/src/Completion.hxx
+++ b/src/Completion.hxx
@@ -59,7 +59,7 @@ public:
 		Range range;
 	};
 
-	Result Complete(const std::string &prefix) const noexcept;
+	Result Complete(std::string_view prefix) const noexcept;
 
 	virtual void Pre(std::string_view value) noexcept = 0;
 	virtual void Post(std::string_view value, Range range) noexcept = 0;