diff --git a/spec/css/custom_properties/error/bang_in_ident/error b/spec/css/custom_properties/error/bang_in_ident/error
deleted file mode 100644
index b764aab46d..0000000000
--- a/spec/css/custom_properties/error/bang_in_ident/error
+++ /dev/null
@@ -1,3 +0,0 @@
-Error: Invalid CSS after "  --prop: foo": expected "}", was "!bar;"
-        on line 2 of /sass/spec/css/custom_properties/error/bang_in_ident/input.scss
-  Use --trace for backtrace.
diff --git a/spec/css/custom_properties/error/bang_in_ident/error-dart-sass b/spec/css/custom_properties/error/bang_in_ident/error-dart-sass
deleted file mode 100644
index aae46c4375..0000000000
--- a/spec/css/custom_properties/error/bang_in_ident/error-dart-sass
+++ /dev/null
@@ -1,4 +0,0 @@
-Error: expected ";".
-  --prop: foo!bar;
-             ^
-  spec/css/custom_properties/error/bang_in_ident/input.scss 2:14  root stylesheet
diff --git a/spec/css/custom_properties/error/bang_in_ident/expected_output.css b/spec/css/custom_properties/error/bang_in_ident/expected_output.css
deleted file mode 100644
index e69de29bb2..0000000000
diff --git a/spec/css/custom_properties/error/bang_in_ident/input.scss b/spec/css/custom_properties/error/bang_in_ident/input.scss
deleted file mode 100644
index 8e6e438145..0000000000
--- a/spec/css/custom_properties/error/bang_in_ident/input.scss
+++ /dev/null
@@ -1,3 +0,0 @@
-.bang-in-ident {
-  --prop: foo!bar;
-}
\ No newline at end of file
diff --git a/spec/css/custom_properties/error/bang_in_ident/status b/spec/css/custom_properties/error/bang_in_ident/status
deleted file mode 100644
index b44fe09a7a..0000000000
--- a/spec/css/custom_properties/error/bang_in_ident/status
+++ /dev/null
@@ -1 +0,0 @@
-65
\ No newline at end of file
diff --git a/spec/css/custom_properties/error/top_level_bang/error b/spec/css/custom_properties/error/top_level_bang/error
deleted file mode 100644
index b8bd7ec83f..0000000000
--- a/spec/css/custom_properties/error/top_level_bang/error
+++ /dev/null
@@ -1,3 +0,0 @@
-Error: Invalid CSS after "  --prop: ": expected "}", was "!;"
-        on line 2 of /sass/spec/css/custom_properties/error/top_level_bang/input.scss
-  Use --trace for backtrace.
diff --git a/spec/css/custom_properties/error/top_level_bang/error-dart-sass b/spec/css/custom_properties/error/top_level_bang/error-dart-sass
deleted file mode 100644
index a2d45fae9e..0000000000
--- a/spec/css/custom_properties/error/top_level_bang/error-dart-sass
+++ /dev/null
@@ -1,4 +0,0 @@
-Error: expected ";".
-  --prop: !;
-          ^
-  spec/css/custom_properties/error/top_level_bang/input.scss 2:11  root stylesheet
diff --git a/spec/css/custom_properties/error/top_level_bang/error-libsass b/spec/css/custom_properties/error/top_level_bang/error-libsass
deleted file mode 100644
index 939e971b28..0000000000
--- a/spec/css/custom_properties/error/top_level_bang/error-libsass
+++ /dev/null
@@ -1,3 +0,0 @@
-Error: Invalid CSS after "  --prop:": expected "}", was "!;"
-        on line 2 of /sass/spec/css/custom_properties/error/top_level_bang/input.scss
-  Use --trace for backtrace.
diff --git a/spec/css/custom_properties/error/top_level_bang/expected_output.css b/spec/css/custom_properties/error/top_level_bang/expected_output.css
deleted file mode 100644
index e69de29bb2..0000000000
diff --git a/spec/css/custom_properties/error/top_level_bang/input.scss b/spec/css/custom_properties/error/top_level_bang/input.scss
deleted file mode 100644
index 1be6462c9a..0000000000
--- a/spec/css/custom_properties/error/top_level_bang/input.scss
+++ /dev/null
@@ -1,3 +0,0 @@
-.top-level-bang {
-  --prop: !;
-}
\ No newline at end of file
diff --git a/spec/css/custom_properties/error/top_level_bang/status b/spec/css/custom_properties/error/top_level_bang/status
deleted file mode 100644
index b44fe09a7a..0000000000
--- a/spec/css/custom_properties/error/top_level_bang/status
+++ /dev/null
@@ -1 +0,0 @@
-65
\ No newline at end of file
diff --git a/spec/css/custom_properties/exclamation/expected_output.css b/spec/css/custom_properties/exclamation/expected_output.css
new file mode 100644
index 0000000000..2ff8581891
--- /dev/null
+++ b/spec/css/custom_properties/exclamation/expected_output.css
@@ -0,0 +1,8 @@
+.exclamation {
+  --important: value !important;
+  --multiple: !important !important;
+  --other-word: !something;
+  --in-identifier: foo!bar;
+  --just-exclam: !;
+  --just-exclams: !!!!!!!;
+}
diff --git a/spec/css/custom_properties/exclamation/input.scss b/spec/css/custom_properties/exclamation/input.scss
new file mode 100644
index 0000000000..0bbb56c551
--- /dev/null
+++ b/spec/css/custom_properties/exclamation/input.scss
@@ -0,0 +1,14 @@
+.exclamation {
+  // `!` is technically not allowed at the top-level of a custom property, but
+  // that's only because `!important` is filtered out before the custom property
+  // is parsed by the CSS parser. As far as Sass is concerned, it's fine.
+  --important: value !important;
+
+  // We even allow constructions like these for forwards-compatibility with
+  // additional flags or syntax CSS might add.
+  --multiple: !important !important;
+  --other-word: !something;
+  --in-identifier: foo!bar;
+  --just-exclam: !;
+  --just-exclams: !!!!!!!;
+}
diff --git a/spec/css/custom_properties/exclamation/options.yml b/spec/css/custom_properties/exclamation/options.yml
new file mode 100644
index 0000000000..32792ae3c6
--- /dev/null
+++ b/spec/css/custom_properties/exclamation/options.yml
@@ -0,0 +1,3 @@
+---
+:todo:
+- libsass