diff --git a/doc/manual/nix-store.xml b/doc/manual/nix-store.xml
index 63ddef28e..416438a0b 100644
--- a/doc/manual/nix-store.xml
+++ b/doc/manual/nix-store.xml
@@ -296,8 +296,12 @@ options control what gets deleted and in what order:
   <varlistentry><term><option>--max-freed</option> <replaceable>bytes</replaceable></term>
   
     <listitem><para>Keep deleting paths until at least
-    <replaceable>bytes</replaceable> bytes have been
-    deleted, then stop.</para></listitem>
+    <replaceable>bytes</replaceable> bytes have been deleted, then
+    stop.  The argument <replaceable>bytes</replaceable> can be
+    followed by the multiplicative suffix <literal>K</literal>,
+    <literal>M</literal>, <literal>G</literal> or
+    <literal>T</literal>, denoting KiB, MiB, GiB or TiB
+    units.</para></listitem>
     
   </varlistentry>
 
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index ff89e8638..b29b08bb5 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -4,6 +4,8 @@
 
 #include <signal.h>
 
+#include <locale>
+
 
 /* These are not implemented here, but must be implemented by a
    program linking against libmain. */
@@ -35,14 +37,27 @@ void printMissing(const PathSet & willBuild,
     unsigned long long downloadSize, unsigned long long narSize);
 
 template<class N> N getIntArg(const string & opt,
-    Strings::iterator & i, const Strings::iterator & end)
+    Strings::iterator & i, const Strings::iterator & end, bool allowUnit)
 {
     ++i;
     if (i == end) throw UsageError(format("`%1%' requires an argument") % opt);
+    string s = *i;
+    N multiplier = 1;
+    if (allowUnit && !s.empty()) {
+        char u = std::toupper(*s.rbegin());
+        if (std::isalpha(u)) {
+            if (u == 'K') multiplier = 1ULL << 10;
+            else if (u == 'M') multiplier = 1ULL << 20;
+            else if (u == 'G') multiplier = 1ULL << 30;
+            else if (u == 'T') multiplier = 1ULL << 40;
+            else throw UsageError(format("invalid unit specifier `%1%'") % u);
+            s.resize(s.size() - 1);
+        }
+    }
     N n;
-    if (!string2Int(*i, n))
+    if (!string2Int(s, n))
         throw UsageError(format("`%1%' requires an integer argument") % opt);
-    return n;
+    return n * multiplier;
 }
 
 /* Show the manual page for the specified program. */
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 365ffa19a..e969a3b71 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -619,7 +619,7 @@ static void opGC(Strings opFlags, Strings opArgs)
         else if (*i == "--print-dead") options.action = GCOptions::gcReturnDead;
         else if (*i == "--delete") options.action = GCOptions::gcDeleteDead;
         else if (*i == "--max-freed") {
-            long long maxFreed = getIntArg<long long>(*i, i, opFlags.end());
+            long long maxFreed = getIntArg<long long>(*i, i, opFlags.end(), true);
             options.maxFreed = maxFreed >= 0 ? maxFreed : 0;
         }
         else throw UsageError(format("bad sub-operation `%1%' in GC") % *i);