Index: Makefile.in
==================================================================
--- Makefile.in
+++ Makefile.in
@@ -34,11 +34,11 @@
 TCC = @CC@
 
 #### Tcl shell for use in running the fossil testsuite.  If you do not
 #    care about testing the end result, this can be blank.
 #
-TCLSH = tclsh
+TCLSH = @TCLSH@
 
 CFLAGS = @CFLAGS@
 LIB =	@LDFLAGS@ @EXTRA_LDFLAGS@ @LIBS@
 BCCFLAGS =	@CPPFLAGS@ $(CFLAGS)
 TCCFLAGS =	@EXTRA_CFLAGS@ @CPPFLAGS@ $(CFLAGS) -DHAVE_AUTOCONFIG_H -D_HAVE_SQLITE_CONFIG_H

Index: auto.def
==================================================================
--- auto.def
+++ auto.def
@@ -33,12 +33,47 @@
 }
 
 # Use pread/pwrite system calls in place of seek + read/write if possible
 define USE_PREAD [cc-check-functions pread]
 
-# Find tclsh for the test suite. Can't yet use jimsh for this.
+# Find tclsh for the test suite.
+#
+# We can't use jimsh for this: the test suite uses features of Tcl that
+# Jim doesn't support, either statically or due to the way it's built by
+# autosetup.  For example, Jim supports `file normalize`, but only if
+# you build it with HAVE_REALPATH, which won't ever be defined in this
+# context because autosetup doesn't try to discover platform-specific
+# details like that before it decides to build jimsh0.  Besides which,
+# autosetup won't build jimsh0 at all if it can find tclsh itself.
+# Ironically, this means we may right now be running under either jimsh0
+# or a version of tclsh that we find unsuitable below!
 cc-check-progs tclsh
+set hbtd /usr/local/Cellar/tcl-tk
+if {[string equal false [get-define TCLSH]]} {
+    msg-result "WARNING: 'make test' will not run here."
+} else {
+    set v [exec /bin/sh -c "echo 'puts \$tcl_version' | tclsh"]
+    if {[expr $v >= 8.6]} {
+        msg-result "Found Tclsh version $v in the PATH."
+        define TCLSH tclsh
+    } elseif {[file isdirectory $hbtd]} {
+        # This is a macOS system with the Homebrew version of Tcl/Tk
+        # installed.  Select the newest version.  It won't normally be
+        # in the PATH to avoid shadowing /usr/bin/tclsh, and even if it
+        # were in the PATH, it's bad practice to put /usr/local/bin (the
+        # Homebrew default) ahead of /usr/bin, especially given that
+        # it's user-writeable by default with Homebrew.  Thus, we can be
+        # pretty sure the only way to call it is with an absolute path.
+        set v [exec ls -tr $hbtd | tail -1]
+        set path "$hbtd/$v/bin/tclsh"
+        define TCLSH $path
+        msg-result "Using Homebrew Tcl/Tk version $path."
+    } else {
+        msg-result "WARNING: tclsh $v found; need >= 8.6 for 'make test'."
+        define TCLSH false     ;# force "make test" failure via /usr/bin/false
+    }
+}
 
 define EXTRA_CFLAGS "-Wall"
 define EXTRA_LDFLAGS ""
 define USE_SYSTEM_SQLITE 0
 define USE_LINENOISE 0

Index: test/tester.tcl
==================================================================
--- test/tester.tcl
+++ test/tester.tcl
@@ -20,10 +20,14 @@
 #     tclsh ../test/tester.tcl ../bld/fossil
 #
 # Where ../test/tester.tcl is the name of this file and ../bld/fossil
 # is the name of the executable to be tested.
 #
+
+# We use some things introduced in 8.6 such as lmap.  auto.def should
+# have found us a suitable Tcl installation.
+package require Tcl 8.6
 
 set testfiledir [file normalize [file dirname [info script]]]
 set testrundir [pwd]
 set testdir [file normalize [file dirname $argv0]]
 set fossilexe [file normalize [lindex $argv 0]]