Index: library/nx/nx.tcl
===================================================================
diff -u -ra7b9d926225de93177a59bc1f2a6daf5228923c3 -r36a0f29d6f1ea1fde0810d05a1fedf3602b865cc
--- library/nx/nx.tcl	(.../nx.tcl)	(revision a7b9d926225de93177a59bc1f2a6daf5228923c3)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision 36a0f29d6f1ea1fde0810d05a1fedf3602b865cc)
@@ -2319,6 +2319,9 @@
   }
 
   ::nx::VariableSlot public method value=delete {obj prop -nocomplain:switch value} {
+    if {![:isMultivalued]} {
+      return -code error "property $prop of [set :domain] is not multivalued"
+    }
     set old [::nsf::var::get $obj $prop]
     set p [lsearch -glob $old $value]
     if {$p > -1} {
Index: tests/properties.test
===================================================================
diff -u -r13ac2740ff99a0438d547250401ac9ed981c58bf -r36a0f29d6f1ea1fde0810d05a1fedf3602b865cc
--- tests/properties.test	(.../properties.test)	(revision 13ac2740ff99a0438d547250401ac9ed981c58bf)
+++ tests/properties.test	(.../properties.test)	(revision 36a0f29d6f1ea1fde0810d05a1fedf3602b865cc)
@@ -163,9 +163,11 @@
 
   set unknowns "valid are: {assign definition destroy get getParameterSpec getPropertyDefinitionOptions onError parameter reconfigure setCheckedInstVar}"
   ? {c1 b add x} {property b of ::C is not multivalued}
+  ? {c1 b delete x} {property b of ::C is not multivalued}
   #? {c1 b add x} "method 'add' unknown for slot ::C::slot::b; $unknowns"
   ? {c1 c add x} {::c1: unable to dispatch method 'c'}
   ? {c1 eval {:c add x}} {property c of ::C is not multivalued}
+  ? {c1 eval {:c delete x}} {property c of ::C is not multivalued}
   #? {c1 eval {:c add x}} "method 'add' unknown for slot ::C::slot::c; $unknowns"
   ? {c1 d add x} {::c1: unable to dispatch method 'd'}
   ? {c1 eval {:d add x}} {::c1: unable to dispatch method 'd'}
@@ -178,9 +180,11 @@
 
   ? {c1 va add x} {::c1: unable to dispatch method 'va'}
   ? {c1 vb add x} {property vb of ::C is not multivalued}
+  ? {c1 vb delete x} {property vb of ::C is not multivalued}
   #? {c1 vb add x} "method 'add' unknown for slot ::C::slot::vb; $unknowns"
   ? {c1 vc add x} {::c1: unable to dispatch method 'vc'}
   ? {c1 eval {:vc add x}} {property vc of ::C is not multivalued}
+  ? {c1 eval {:vc delete x}} {property vc of ::C is not multivalued}
   #? {c1 eval {:vc add x}} "method 'add' unknown for slot ::C::slot::vc; $unknowns"
   ? {c1 vd add x} {::c1: unable to dispatch method 'vd'}
   ? {c1 eval {:vd add x}} {::c1: unable to dispatch method 'vd'}