diff --git a/bin/build.sh b/bin/build.sh
index c3d6cfd..6324d85 100755
--- a/bin/build.sh
+++ b/bin/build.sh
@@ -36,7 +36,7 @@ for t in lib/*.d.ts; do
     sed -i '.tmp' -e 's/split(text: string): any;/split(text: string): string[];/g' $t
     sed -i '.tmp' -e 's/splitn(text: string, limit: number): any;/splitn(text: string, limit: number): string[];/g' $t
     sed -i '.tmp' -e 's/syntax(): any;/syntax(): Hir;/g' $t
-    sed -i '.tmp' -e 's/captureNames(): any\[\];/captureNames(): string[];/g' $t
+    sed -i '.tmp' -e 's/captureNames(): any\[\];/captureNames(): (string | null)[];/g' $t
     sed -i '.tmp' -e 's/captures(text: string): any;/captures(text: string): Captures | undefined;/g' $t
     sed -i '.tmp' -e 's/capturesAll(text: string): any;/capturesAll(text: string): Captures[];/g' $t
     sed -i '.tmp' -e 's/matches(text: string): any\[\];/matches(text: string): number[];/g' $t
@@ -48,7 +48,7 @@ for t in lib/*.d.ts; do
     sed -i -e 's/split(text: string): any;/split(text: string): string[];/g' $t
     sed -i -e 's/splitn(text: string, limit: number): any;/splitn(text: string, limit: number): string[];/g' $t
     sed -i -e 's/syntax(): any;/syntax(): Hir;/g' $t
-    sed -i -e 's/captureNames(): any\[\];/captureNames(): string[];/g' $t
+    sed -i -e 's/captureNames(): any\[\];/captureNames(): (string | null)[];/g' $t
     sed -i -e 's/captures(text: string): any;/captures(text: string): Captures | undefined;/g' $t
     sed -i -e 's/capturesAll(text: string): any;/capturesAll(text: string): Captures[];/g' $t
     sed -i -e 's/matches(text: string): any\[\];/matches(text: string): number[];/g' $t
diff --git a/src/rregex.rs b/src/rregex.rs
index ab0d782..a6916f0 100644
--- a/src/rregex.rs
+++ b/src/rregex.rs
@@ -152,7 +152,10 @@ impl RRegex {
     pub fn capture_names(&self) -> Vec<JsValue> {
         self.regex
             .capture_names()
-            .filter_map(|item| item.map(JsValue::from))
+            .map(|item| match item {
+                Some(name) => JsValue::from(name),
+                None => JsValue::NULL,
+            })
             .collect()
     }
 
diff --git a/test/rregex.test.ts b/test/rregex.test.ts
index 005d9d3..a750899 100644
--- a/test/rregex.test.ts
+++ b/test/rregex.test.ts
@@ -121,6 +121,7 @@ describe(`RRegex`, () => {
   test(`captureNames`, () => {
     const regex = new RRegex('(?P<y>\\d{4})-(?P<m>\\d{2})-(?P<d>\\d{2})')
     expect(regex.captureNames()).toEqual([
+      null,
       "y",
       "m",
       "d",