diff --git a/pkgs/build-support/vm/windows/bootstrap.nix b/pkgs/build-support/vm/windows/bootstrap.nix
index 47afce5b5a37..e3b44d1b6ab7 100644
--- a/pkgs/build-support/vm/windows/bootstrap.nix
+++ b/pkgs/build-support/vm/windows/bootstrap.nix
@@ -1,6 +1,6 @@
 { stdenv, fetchurl, vmTools, writeScript, writeText, runCommand, makeInitrd
 , python, perl, coreutils, dosfstools, gzip, mtools, netcat, openssh, qemu
-, samba, socat, vde2, cdrkit, pathsFromGraph
+, samba, socat, vde2, cdrkit, pathsFromGraph, gnugrep
 }:
 
 { isoFile, productKey, arch ? null }:
@@ -10,7 +10,7 @@ with stdenv.lib;
 let
   controller = import ./controller {
     inherit stdenv writeScript vmTools makeInitrd;
-    inherit samba vde2 openssh socat netcat coreutils gzip;
+    inherit samba vde2 openssh socat netcat coreutils gzip gnugrep;
   };
 
   mkCygwinImage = import ./cygwin-iso {
diff --git a/pkgs/build-support/vm/windows/controller/default.nix b/pkgs/build-support/vm/windows/controller/default.nix
index ee9bf0286943..0beaf401758a 100644
--- a/pkgs/build-support/vm/windows/controller/default.nix
+++ b/pkgs/build-support/vm/windows/controller/default.nix
@@ -1,5 +1,5 @@
 { stdenv, writeScript, vmTools, makeInitrd
-, samba, vde2, openssh, socat, netcat, coreutils, gzip
+, samba, vde2, openssh, socat, netcat, coreutils, gnugrep, gzip
 }:
 
 { sshKey
@@ -217,17 +217,26 @@ let
     fi
   '';
 
+  toMonitor = "${socat}/bin/socat - UNIX-CONNECT:$MONITOR_SOCKET";
+
   postVM = if suspendTo != null then ''
     while ! test -e "$XCHG_DIR/suspend_now"; do
       ${checkDropOut}
       ${coreutils}/bin/sleep 1
     done
-    ${socat}/bin/socat - UNIX-CONNECT:$MONITOR_SOCKET <<CMD
+    ${toMonitor} <<CMD
     stop
     migrate_set_speed 4095m
     migrate "exec:${gzip}/bin/gzip -c > '${suspendTo}'"
-    quit
     CMD
+    echo -n "Waiting for memory dump to finish..."
+    while ! echo info migrate | ${toMonitor} | \
+          ${gnugrep}/bin/grep -qi '^migration *status: *complete'; do
+      ${coreutils}/bin/sleep 1
+      echo -n .
+    done
+    echo " done."
+    echo quit | ${toMonitor}
     wait $(< "$WINVM_PIDFILE")
     eval "$postVM"
     exit 0
diff --git a/pkgs/build-support/vm/windows/default.nix b/pkgs/build-support/vm/windows/default.nix
index f9b44d450d99..f9f1d75c70d6 100644
--- a/pkgs/build-support/vm/windows/default.nix
+++ b/pkgs/build-support/vm/windows/default.nix
@@ -5,6 +5,7 @@ let
     inherit (pkgs) stdenv vmTools writeScript writeText runCommand makeInitrd;
     inherit (pkgs) coreutils dosfstools gzip mtools netcat openssh qemu samba;
     inherit (pkgs) socat vde2 fetchurl python perl cdrkit pathsFromGraph;
+    inherit (pkgs) gnugrep;
   };
 
   builder = ''