diff --git a/src/lib.rs b/src/lib.rs
index 4b0b8539..0330a20d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -23101,6 +23101,22 @@ mod tests {
     minify_test(".foo { --test: .5s; }", ".foo{--test:.5s}");
     minify_test(".foo { --theme-sizes-1\\/12: 2 }", ".foo{--theme-sizes-1\\/12:2}");
     minify_test(".foo { --test: 0px; }", ".foo{--test:0px}");
+    test(
+      ".foo { transform: var(--bar, ) }",
+      indoc! {r#"
+      .foo {
+        transform: var(--bar, );
+      }
+      "#},
+    );
+    test(
+      ".foo { transform: env(--bar, ) }",
+      indoc! {r#"
+      .foo {
+        transform: env(--bar, );
+      }
+      "#},
+    );
 
     // Test attr() function with type() syntax - minified
     minify_test(
diff --git a/src/properties/custom.rs b/src/properties/custom.rs
index 2280b37f..9ffb838d 100644
--- a/src/properties/custom.rs
+++ b/src/properties/custom.rs
@@ -1215,7 +1215,10 @@ impl<'i> Variable<'i> {
     dest.write_str("var(")?;
     self.name.to_css(dest)?;
     if let Some(fallback) = &self.fallback {
-      dest.delim(',', false)?;
+      dest.write_char(',')?;
+      if !fallback.starts_with_whitespace() {
+        dest.whitespace()?;
+      }
       fallback.to_css(dest, is_custom_property)?;
     }
     dest.write_char(')')
@@ -1389,7 +1392,10 @@ impl<'i> EnvironmentVariable<'i> {
     }
 
     if let Some(fallback) = &self.fallback {
-      dest.delim(',', false)?;
+      dest.write_char(',')?;
+      if !fallback.starts_with_whitespace() {
+        dest.whitespace()?;
+      }
       fallback.to_css(dest, is_custom_property)?;
     }
     dest.write_char(')')