index e6b9591..e655934 100644
--- lib/app-critcl/runtime.tcl.orig
+++ lib/app-critcl/runtime.tcl
@@ -117,8 +117,19 @@ proc ::critcl::runtime::MapPlatform {{mapping {}}} {
 	set v [split $version .]
 	set v1 [lindex $v 0]
 	set v2 [lindex $v 1]
-	incr v1 -4
-	set version 10.$v1.$v2
+	set v3 [lindex $v 2]
+	# Darwin 19 and earlier are macOS 10.x. Darwin 20-24 are macOS
+    # 11-15. Darwin 25 is macOS 26.
+    if {$v1 >= 25} {
+        incr v1
+        set version $v1.$v2.$v3
+    } elseif {$v1 >= 20} {
+        incr v1 -9
+        set version $v1.$v2.$v3
+    } else {
+        incr v1 -4
+        set version 10.$v1.$v2
+	}
     } else {
 	# Strip trailing non-version info
 	regsub -- {-.*$} $version {} version
diff --git a/lib/critcl-platform/platform.tcl b/lib/critcl-platform/platform.tcl
index fbfc535..d2a84b6 100644
--- lib/critcl-platform/platform.tcl.orig
+++ lib/critcl-platform/platform.tcl
@@ -183,9 +183,19 @@ proc ::platform::identify {} {
 	macosx {
 	    set major [lindex [split $tcl_platform(osVersion) .] 0]
 	    if {$major > 8} {
-		incr major -4
-		append plat 10.$major
-		return "${plat}-${cpu}"
+	        # Darwin 19 and earlier are macOS 10.x. Darwin 20-24
+            # are macOS 11-15. Darwin 25 is macOS 26.
+           if {$major >= 25} {
+               incr major
+               append plat $major
+	        } elseif {$major >= 20} {
+	            incr major -9
+		        append plat $major
+	        } else {
+	            incr major -4
+		        append plat 10.$major
+	        }
+		    return "${plat}-${cpu}"
 	    }
 	}
 	linux {
index f4d1fd3..907cdf6 100644
--- lib/critcl/Config.in.orig
+++ lib/critcl/Config.in
@@ -129,8 +129,15 @@ if {[string match macosx-* $platform]} {
     } else {
         # use the current platform
         foreach {v1 v2 v3} [split $::tcl_platform(osVersion) .] break
-        incr v1 -4
-        set osxmin 10.$v1.$v2
+        # Darwin 19 and earlier are macOS 10.x. Darwin 20 and later are macOS
+        # 11, macOS 12, etc.
+        if {$v1 >= 20} {
+            incr v1 -9
+            set osxmin ${v1}.0
+        } else {
+            incr v1 -4
+            set osxmin 10.$v1
+        }
         # do we actually need to check if universal is supported, given the
         # gcc check below will do it for us?
         # set info [exec lipo -info /usr/lib/libSystem.dylib]