diff --git a/src/Lambert.f90 b/src/Lambert.f90
index 9b7d2ef86..da0c0b3aa 100644
--- a/src/Lambert.f90
+++ b/src/Lambert.f90
@@ -44,6 +44,7 @@ module Lambert
     PI
   use future
 
+  implicit none
   private
   real(pReal), parameter, private :: &
     SPI  = sqrt(PI), &