diff --git a/tests/runtests.pl b/tests/runtests.pl
index 897a04cbdffb6b91fee14b1998e6e4bb5c08844b..17089ae546b9ec64e511753525ced96534c3ec29 100755
--- a/tests/runtests.pl
+++ b/tests/runtests.pl
@@ -87,6 +87,19 @@ chomp($pwd = `pwd`);
 $ENV{'CURL_MEMDEBUG'} = 1;
 $ENV{'HOME'}=$pwd;
 
+##########################################################################
+# Clear all possible '*_proxy' environment variables for various protocols
+# to prevent them to interfere with our testing!
+
+my $protocol;
+foreach $protocol (('ftp', 'http', 'ftps', 'https', 'gopher', 'no')) {
+    my $proxy = "${protocol}_proxy";
+    # clear lowercase version
+    $ENV{$proxy}=undef;
+    # clear uppercase version
+    $ENV{uc($proxy)}=undef;
+}
+
 #######################################################################
 # Return the pid of the server as found in the given pid file
 #