diff --git a/build/ka10/include.tcl b/build/ka10/include.tcl
index 2d5e59d7..b0dbd3e7 100644
--- a/build/ka10/include.tcl
+++ b/build/ka10/include.tcl
@@ -191,3 +191,19 @@ proc translate_diagnostics {} {
     respond "*" "\033\024"
     respond " " "dsk: maint; part k, part k.old\r"
 }
+
+proc patch_clib_16 {} {
+    respond "*" ":job clib\r"
+    respond "*" "\033\060l"
+    respond " " "c; \[clib\] 16\r"
+    respond "*" "23237/"
+    respond "FIX" "ufa 1,775763\n"
+    respond "JRST" "tlo 2,777000\r"
+    respond "\n" "23244/"
+    respond "FIX" "ufa 1,775763\n"
+    respond "MOVN" "tlo 2,777000\n"
+    respond "JRST" "movn 2,2\r"
+    respond "\n" "\033\060y"
+    respond " " "c; \[clib\] 16\r"
+    respond "*" ":kill\r"
+}
diff --git a/build/ks10/include.tcl b/build/ks10/include.tcl
index e25e9654..b8a73618 100644
--- a/build/ks10/include.tcl
+++ b/build/ks10/include.tcl
@@ -198,3 +198,6 @@ proc translate_diagnostics {} {
     respond "*" "\033\024"
     respond " " "dsk: maint; part k, part l\r"
 }
+
+proc patch_clib_16 {} {
+}
diff --git a/build/misc.tcl b/build/misc.tcl
index 3fc9018b..9b94d94f 100644
--- a/build/misc.tcl
+++ b/build/misc.tcl
@@ -1434,6 +1434,9 @@ respond "*" ":link sys3; ts r, r; ts r42\r"
 # r; rmacro 1 -> r; r macros
 # sys3; ts itype -> r; ts itype
 
+# Revert patch to [CLIB] 16 to avoid use of the FIX instruction on a KA10.
+patch_clib_16
+
 # C library for drawing on a TV display.
 respond "*" ":cwd clib\r"
 respond "*" ":cc tv.>\r"