diff --git a/Syntax/Just.sublime-syntax b/Syntax/Just.sublime-syntax
index 85b1266..8552cbc 100644
--- a/Syntax/Just.sublime-syntax
+++ b/Syntax/Just.sublime-syntax
@@ -19,7 +19,7 @@ file_extensions:
 variables:
   valid_name: "[a-zA-Z_][a-zA-Z0-9_-]*"
   built_in_functions: |
-    (?x)  # ignore whitespace in this regex
+    (?x)(?:  # ignore whitespace in this regex
 
       absolute_path | arch | capitalize | clean | env_var_or_default | env_var |
       error | extension | file_name | file_stem | invocation_directory_native |
@@ -31,17 +31,20 @@ variables:
       trim_end_matches | trim_end_match | trim_end | trim_start_matches |
       trim_start_match | trim_start | trim | uppercase | uppercamelcase |
       uuid | without_extension
-
+    )
   boolean_settings: |
-    (?x)
+    (?x)(?:
       allow-duplicate-recipes | dotenv-load | export | fallback | ignore-comments |
       positional-arguments | windows-powershell
+    )
   string_settings: |
-    (?x)
+    (?x)(?:
       tempdir
+    )
   shell_settings: |
-    (?x)
+    (?x)(?:
       shell | windows-shell
+    )
   recipe_attributes: |
     (?x)
       linux | macos | no-cd | no-exit-message | private | unix | windows
@@ -274,6 +277,11 @@ contexts:
   ###[ VARIABLES ]###############################################################
 
   operands-variables:
+    # First check for an invalid function
+    - match: '\b({{valid_name}})\b\s*(\()'
+      captures:
+        1: source.just
+        2: invalid.illegal.just
     - match: \b(?:{{valid_name}})\b
       scope: variable.other.just
 
@@ -503,10 +511,17 @@ contexts:
     - match: '^set(?=\s+)'
       scope: storage.modifier.definition.just
       push:
+        - settings-invalid
         - settings-boolean
         - settings-shell
         - settings-string
 
+  settings-invalid:
+    - match: '\b({{valid_name}})\b\s*:='
+      captures:
+        1: invalid.illegal.just
+    - include: else-pop
+
   settings-boolean:
     - match: '\b{{boolean_settings}}\b'
       scope: entity.name.definition.just
@@ -532,8 +547,9 @@ contexts:
     - include: else-pop
 
   constant-boolean:
-    - match: "(true|false)"
-      scope: constant.language.boolean.just
+    - match: '\b(true|false)\b'
+      captures:
+        1: constant.language.boolean.just
       pop: 1
     - include: else-pop
 
diff --git a/Syntax/tests/syntax_test_just.functions.just b/Syntax/tests/syntax_test_just.functions.just
index 86a0369..a404b6e 100644
--- a/Syntax/tests/syntax_test_just.functions.just
+++ b/Syntax/tests/syntax_test_just.functions.just
@@ -216,3 +216,11 @@ upper := uppercase("test-me")
 #                  ^^^^^^^^^ string.quoted.double.just
 #                           ^ meta.function-call.arguments.just punctuation.section.group.end.just
 
+
+#
+# Invalid cases
+#
+
+t2 := titlecased("test me thanks" + lowercase("blah"))
+#     ^^^^^^^^^^ - meta.function-call.identifier.just - support.function.builtin.just - variable.other.just
+#               ^ invalid.illegal.just 
diff --git a/Syntax/tests/syntax_test_just.settings.just b/Syntax/tests/syntax_test_just.settings.just
index 5977037..8aa6cce 100644
--- a/Syntax/tests/syntax_test_just.settings.just
+++ b/Syntax/tests/syntax_test_just.settings.just
@@ -75,3 +75,31 @@ set ignore-comments # Comment
 #   ^^^^^^^^^^^^^^^ entity.name.definition.just
 #                   ^^ comment.line.number-sign.just punctuation.definition.comment.begin.just
 #                    ^^^^^^^^ comment.line.number-sign.just
+
+
+#
+# Invalid cases
+#
+
+# Extra characters for boolean setting
+set exported
+#^^ storage.modifier.definition.just
+#   ^^^^^^^^^ - entity.name.definition.just - variable.other.just
+
+# Extra characters for string setting
+set tempdirectory := '/tmp'
+#   ^^^^^^^^^^^^^ invalid.illegal.just - entity.name.definition.just - variable.other.just
+
+set shellac := ["sh", "-c"]
+#   ^^^^^^^ invalid.illegal.just - entity.name.definition.just - variable.other.just
+
+# Wrong character case
+set tempDir
+#^^ storage.modifier.definition.just
+#   ^^^^^^^^ - entity.name.definition.just - variable.other.just
+
+set export := trued
+#             ^^^^^ - constant.language.boolean.just
+
+set dotenv-load := falsey
+#                  ^^^^^^ - constant.language.boolean.just