diff --git a/mozglue/misc/decimal/Decimal.cpp b/mozglue/misc/decimal/Decimal.cpp
--- a/mozglue/misc/decimal/Decimal.cpp
+++ b/mozglue/misc/decimal/Decimal.cpp
@@ -25,16 +25,17 @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "Decimal.h"
 #include "moz-decimal-utils.h"
+#include "DoubleConversion.h"
 
 using namespace moz_decimal_utils;
 
 #include <algorithm>
 #include <float.h>
 
 namespace blink {
 
@@ -1043,8 +1044,20 @@ bool Decimal::toString(char* strBuf, siz
 }
 
 Decimal Decimal::zero(Sign sign)
 {
     return Decimal(EncodedData(sign, EncodedData::ClassZero));
 }
 
 } // namespace blink
+
+// Implementation of DoubleConversion.h:
+
+namespace mozilla {
+
+Maybe<double> StringToDouble(Span<const char> aStringSpan) {
+    bool valid = false;
+    double result = mozToDouble(aStringSpan, &valid);
+    return valid ? Some(result) : Nothing();
+}
+
+}