diff --git a/syntax/just.vim b/syntax/just.vim
index 6e0e907..2db9874 100644
--- a/syntax/just.vim
+++ b/syntax/just.vim
@@ -274,6 +274,8 @@ syn match justConditionalOperator "\V=~"
 
 syn match justOperator "\V+"
 syn match justOperator "\V/"
+syn match justOperator "\V&&"
+syn match justOperator "\V||"
 
 syn keyword justConstant
    \ HEX HEXLOWER HEXUPPER
diff --git a/tests/cases/script.html b/tests/cases/unstable.html
similarity index 75%
rename from tests/cases/script.html
rename to tests/cases/unstable.html
index bcf54d0..0d74452 100644
--- a/tests/cases/script.html
+++ b/tests/cases/unstable.html
@@ -1,3 +1,5 @@
+<span class="Statement">set</span> <span class="Keyword">unstable</span>
+
 <span class="Type">[script</span><span class="Operator">:</span> <span class="String">'python3'</span><span class="Type">]</span>
 <span class="Function">python_info</span><span class="Operator">:</span>
 <span class="Number">&Tab;import platform</span>
@@ -7,3 +9,5 @@
 <span class="Function">nested_justfile</span><span class="Operator">:</span>
 <span class="Number">&Tab;foo:</span>
 <span class="Number">&Tab;&Tab;pwd</span>
+
+foo <span class="Operator">:=</span> <span class="String">'foo'</span> <span class="Operator">&amp;&amp;</span> <span class="String">''</span> <span class="Operator">||</span> <span class="String">'foo'</span>
diff --git a/tests/cases/script.just b/tests/cases/unstable.just
similarity index 81%
rename from tests/cases/script.just
rename to tests/cases/unstable.just
index 872a71c..4373fd7 100644
--- a/tests/cases/script.just
+++ b/tests/cases/unstable.just
@@ -1,3 +1,5 @@
+set unstable
+
 [script: 'python3']
 python_info:
 	import platform
@@ -7,3 +9,5 @@ python_info:
 nested_justfile:
 	foo:
 		pwd
+
+foo := 'foo' && '' || 'foo'