diff --git a/src/lib/ffmpeg/LibFmt.hxx b/src/lib/ffmpeg/LibFmt.hxx
index aa068711f..dee83ed2d 100644
--- a/src/lib/ffmpeg/LibFmt.hxx
+++ b/src/lib/ffmpeg/LibFmt.hxx
@@ -13,7 +13,7 @@ template<>
 struct fmt::formatter<AVSampleFormat> : formatter<string_view>
 {
 	template<typename FormatContext>
-	auto format(const AVSampleFormat format, FormatContext &ctx) {
+	auto format(const AVSampleFormat format, FormatContext &ctx) const {
 		const char *name = av_get_sample_fmt_name(format);
 		if (name == nullptr)
 			name = "?";
diff --git a/src/lib/fmt/AudioFormatFormatter.hxx b/src/lib/fmt/AudioFormatFormatter.hxx
index e0ffb6216..8da98efd4 100644
--- a/src/lib/fmt/AudioFormatFormatter.hxx
+++ b/src/lib/fmt/AudioFormatFormatter.hxx
@@ -13,7 +13,7 @@ template<>
 struct fmt::formatter<SampleFormat> : formatter<string_view>
 {
 	template<typename FormatContext>
-	auto format(const SampleFormat format, FormatContext &ctx) {
+	auto format(const SampleFormat format, FormatContext &ctx) const {
 		return formatter<string_view>::format(sample_format_to_string(format),
 						      ctx);
 	}
@@ -23,7 +23,7 @@ template<>
 struct fmt::formatter<AudioFormat> : formatter<string_view>
 {
 	template<typename FormatContext>
-	auto format(const AudioFormat &af, FormatContext &ctx) {
+	auto format(const AudioFormat &af, FormatContext &ctx) const {
 		return formatter<string_view>::format(ToString(af).c_str(),
 						      ctx);
 	}
diff --git a/src/lib/fmt/ExceptionFormatter.hxx b/src/lib/fmt/ExceptionFormatter.hxx
index 3f342df67..f08b3bb22 100644
--- a/src/lib/fmt/ExceptionFormatter.hxx
+++ b/src/lib/fmt/ExceptionFormatter.hxx
@@ -12,7 +12,7 @@ template<>
 struct fmt::formatter<std::exception_ptr> : formatter<string_view>
 {
 	template<typename FormatContext>
-	auto format(std::exception_ptr e, FormatContext &ctx) {
+	auto format(std::exception_ptr e, FormatContext &ctx) const {
 		return formatter<string_view>::format(GetFullMessage(e), ctx);
 	}
 };
diff --git a/src/lib/fmt/PathFormatter.hxx b/src/lib/fmt/PathFormatter.hxx
index e5ae89dec..add06df81 100644
--- a/src/lib/fmt/PathFormatter.hxx
+++ b/src/lib/fmt/PathFormatter.hxx
@@ -13,7 +13,7 @@ template<std::convertible_to<Path> T>
 struct fmt::formatter<T> : formatter<string_view>
 {
 	template<typename FormatContext>
-	auto format(Path path, FormatContext &ctx) {
+	auto format(Path path, FormatContext &ctx) const {
 		return formatter<string_view>::format(path.ToUTF8(), ctx);
 	}
 };