diff --git a/src/libutil-tests/file-content-address.cc b/src/libutil-tests/file-content-address.cc
index 5cdf94edc..92c6059a4 100644
--- a/src/libutil-tests/file-content-address.cc
+++ b/src/libutil-tests/file-content-address.cc
@@ -1,3 +1,4 @@
+#include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
 #include "nix/util/file-content-address.hh"
@@ -26,8 +27,11 @@ TEST(FileSerialisationMethod, testRoundTripPrintParse_2) {
     }
 }
 
-TEST(FileSerialisationMethod, testParseFileSerialisationMethodOptException) {
-    EXPECT_THROW(parseFileSerialisationMethod("narwhal"), UsageError);
+TEST(FileSerialisationMethod, testParseFileSerialisationMethodOptException)
+{
+    EXPECT_THAT(
+        []() { parseFileSerialisationMethod("narwhal"); },
+        testing::ThrowsMessage<UsageError>(testing::HasSubstr("narwhal")));
 }
 
 /* ----------------------------------------------------------------------------
@@ -54,8 +58,11 @@ TEST(FileIngestionMethod, testRoundTripPrintParse_2) {
     }
 }
 
-TEST(FileIngestionMethod, testParseFileIngestionMethodOptException) {
-    EXPECT_THROW(parseFileIngestionMethod("narwhal"), UsageError);
+TEST(FileIngestionMethod, testParseFileIngestionMethodOptException)
+{
+    EXPECT_THAT(
+        []() { parseFileIngestionMethod("narwhal"); },
+        testing::ThrowsMessage<UsageError>(testing::HasSubstr("narwhal")));
 }
 
 }
diff --git a/src/libutil/file-content-address.cc b/src/libutil/file-content-address.cc
index 673e1dff1..142bc70d5 100644
--- a/src/libutil/file-content-address.cc
+++ b/src/libutil/file-content-address.cc
@@ -22,7 +22,7 @@ FileSerialisationMethod parseFileSerialisationMethod(std::string_view input)
     if (ret)
         return *ret;
     else
-        throw UsageError("Unknown file serialiation method '%s', expect `flat` or `nar`");
+        throw UsageError("Unknown file serialiation method '%s', expect `flat` or `nar`", input);
 }
 
 
@@ -35,7 +35,7 @@ FileIngestionMethod parseFileIngestionMethod(std::string_view input)
         if (ret)
             return static_cast<FileIngestionMethod>(*ret);
         else
-            throw UsageError("Unknown file ingestion method '%s', expect `flat`, `nar`, or `git`");
+            throw UsageError("Unknown file ingestion method '%s', expect `flat`, `nar`, or `git`", input);
     }
 }