diff --git a/src/libstore/profiles.cc b/src/libstore/profiles.cc
index 75db8f9df..84a21c0ba 100644
--- a/src/libstore/profiles.cc
+++ b/src/libstore/profiles.cc
@@ -212,14 +212,14 @@ void deleteGenerationsOlderThan(const Path & profile, time_t t, bool dryRun)
 void deleteGenerationsOlderThan(const Path & profile, const string & timeSpec, bool dryRun)
 {
     if (timeSpec.empty() || timeSpec[timeSpec.size() - 1] != 'd')
-        throw Error("invalid number of days specifier '%1%', expected something like '14d'", timeSpec);
+        throw UsageError("invalid number of days specifier '%1%', expected something like '14d'", timeSpec);
 
     time_t curTime = time(0);
     string strDays = string(timeSpec, 0, timeSpec.size() - 1);
     auto days = string2Int<int>(strDays);
 
     if (!days || *days < 1)
-        throw Error("invalid number of days specifier '%1%'", timeSpec);
+        throw UsageError("invalid number of days specifier '%1%'", timeSpec);
 
     time_t oldTime = curTime - *days * 24 * 3600;