diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index 5b55d606..e9ed477e 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -4979,6 +4979,16 @@ sub main {
    # Explicit --chunk-size disable auto chunk sizing.
    $o->set('chunk-time', 0) if $o->got('chunk-size');
 
+   foreach my $opt ( qw(max-load critical-load) ) {
+      my $spec = $o->get($opt);
+      eval {
+         MySQLStatusWaiter::_parse_spec($o->get($spec));
+      };
+      if ( $EVAL_ERROR ) {
+         $o->save_error("Invalid --$opt: $spec");
+      }
+   }
+
    if ( !$o->get('help') ) {
       if ( @ARGV ) {
          $o->save_error('Specify only one DSN on the command line');
diff --git a/lib/MySQLStatusWaiter.pm b/lib/MySQLStatusWaiter.pm
index b74c2b9e..0e0ec18a 100644
--- a/lib/MySQLStatusWaiter.pm
+++ b/lib/MySQLStatusWaiter.pm
@@ -45,15 +45,17 @@ sub new {
    }
 
    PTDEBUG && _d('Parsing spec for max thresholds');
-   my $max_val_for = _parse_spec(
-      spec             => $args{max_spec},
+   my $max_val_for = _parse_spec($args{max_spec});
+   _set_initial_vals(
+      vars             => $max_val_for,
       get_status       => $args{get_status},
       threshold_factor => 0.2, # +20%
    );
 
    PTDEBUG && _d('Parsing spec for critical thresholds');
-   my $critical_val_for = _parse_spec(
-      spec             => $args{critical_spec} || [],
+   my $critical_val_for = _parse_spec($args{critical_spec} || []);
+   _set_initial_vals(
+      vars             => $critical_val_for,
       get_status       => $args{get_status},
       threshold_factor => 1.0, # double (x2; +100%)
    );
@@ -79,27 +81,23 @@ sub new {
 # Returns:
 #   Hashref with each variable's maximum permitted value.
 sub _parse_spec {
-   my ( %args ) = @_;
-   my @required_args = qw(spec get_status);
-   foreach my $arg ( @required_args ) {
-      die "I need a $arg argument" unless defined $args{$arg};
-   }
-   my ($spec, $get_status) = @args{@required_args};
+   my ($spec) = @_;
 
    return unless $spec && scalar @$spec;
-   my $threshold_factor = $args{threshold_factor} || 0.20;
 
    my %max_val_for;
    foreach my $var_val ( @$spec ) {
       my ($var, $val) = split /[:=]/, $var_val;
       die "Invalid spec: $var_val" unless $var;
+      
       if ( !$val ) {
-         my $init_val = $get_status->($var);
-         PTDEBUG && _d('Initial', $var, 'value:', $init_val);
-         $val = int(($init_val * $threshold_factor) + $init_val);
+         PTDEBUG && _d('Will get intial value for', $var, 'later');
+         $max_val_for{$var} = undef;
+      }
+      else {
+         PTDEBUG && _d('Wait if', $var, '>=', $val);
+         $max_val_for{$var} = $val;
       }
-      PTDEBUG && _d('Wait if', $var, '>=', $val);
-      $max_val_for{$var} = $val;
    }
 
    return \%max_val_for; 
@@ -192,6 +190,31 @@ sub wait {
    return;
 }
 
+sub _set_initial_vals {
+   my (%args) = @_;
+   my @required_args = qw(vars get_status threshold_factor);
+   foreach my $arg ( @required_args ) {
+      die "I need a $arg argument" unless defined $args{$arg};
+   }
+   my ($vars, $get_status, $threshold_factor) = @args{@required_args};
+
+   PTDEBUG && _d('Setting initial values');
+   return unless $vars && scalar %$vars;
+
+   foreach my $var ( keys %$vars ) {
+      next if defined $vars->{$var};
+   
+      my $init_val = $get_status->($var);
+      PTDEBUG && _d('Initial', $var, 'value:', $init_val);
+      die "Variable does not exist or has undefined value: $var"
+         unless defined $init_val;
+
+      my $val = int(($init_val * $threshold_factor) + $init_val);
+      $vars->{$var} = $val;
+      PTDEBUG && _d('Wait if', $var, '>=', $val);
+   }
+}
+
 sub _d {
    my ($package, undef, $line) = caller 0;
    @_ = map { (my $temp = $_) =~ s/\n/\n# /g; $temp; }
diff --git a/t/lib/MySQLStatusWaiter.t b/t/lib/MySQLStatusWaiter.t
index 3b617818..d7cd22e5 100644
--- a/t/lib/MySQLStatusWaiter.t
+++ b/t/lib/MySQLStatusWaiter.t
@@ -39,6 +39,21 @@ sub sleep {
    return;
 }
 
+# #############################################################################
+# _parse_spec()
+# #############################################################################
+
+throws_ok(
+   sub { new MySQLStatusWaiter(
+      max_spec => '100',
+      get_status => \&get_status,
+      sleep      => \&sleep,
+      oktorun    => \&oktorun,
+   ) },
+   qr/Invalid spec/,
+   "Validate max_spec"
+);
+
 # ############################################################################
 # Use initial vals + 20%.
 # ############################################################################
diff --git a/t/pt-online-schema-change/option_sanity.t b/t/pt-online-schema-change/option_sanity.t
index dbd427b7..99bbe23e 100644
--- a/t/pt-online-schema-change/option_sanity.t
+++ b/t/pt-online-schema-change/option_sanity.t
@@ -9,7 +9,7 @@ BEGIN {
 use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
-use Test::More tests => 6;
+use Test::More tests => 8;
 
 use PerconaTest;
 
@@ -58,6 +58,20 @@ like(
    "Cannot --alter-foreign-keys-method=drop_swap with --no-drop-new-table"
 );
 
+$output = `$cmd h=127.1,P=12345,u=msandbox,p=msandbox,D=mysql,t=user --max-load 100 --alter "ENGINE=MyISAM" --dry-run`;
+like(
+   $output,
+   qr/Invalid --max-load/,
+   "Validates --max-load"
+);
+
+$output = `$cmd h=127.1,P=12345,u=msandbox,p=msandbox,D=mysql,t=user --critical-load 100 --alter "ENGINE=MyISAM" --dry-run`;
+like(
+   $output,
+   qr/Invalid --critical-load/,
+   "Validates --critical-load"
+);
+
 # #############################################################################
 # Done.
 # #############################################################################