diff --git a/package.yaml b/package.yaml
index c67d6a071..b1a776be2 100644
--- a/package.yaml
+++ b/package.yaml
@@ -72,7 +72,7 @@ flags:
 
 when:
   - condition: flag(swift)
-    ghc-options:
+    cpp-options:
       - -DswiftJSON
 
 library:
diff --git a/simplexmq.cabal b/simplexmq.cabal
index c27390aaa..d43a8387d 100644
--- a/simplexmq.cabal
+++ b/simplexmq.cabal
@@ -116,7 +116,7 @@ library
     , x509-store ==1.6.*
     , x509-validation ==1.6.*
   if flag(swift)
-    ghc-options: -DswiftJSON
+    cpp-options: -DswiftJSON
   default-language: Haskell2010
 
 executable smp-agent
@@ -170,7 +170,7 @@ executable smp-agent
     , x509-store ==1.6.*
     , x509-validation ==1.6.*
   if flag(swift)
-    ghc-options: -DswiftJSON
+    cpp-options: -DswiftJSON
   default-language: Haskell2010
 
 executable smp-server
@@ -227,7 +227,7 @@ executable smp-server
     , x509-store ==1.6.*
     , x509-validation ==1.6.*
   if flag(swift)
-    ghc-options: -DswiftJSON
+    cpp-options: -DswiftJSON
   default-language: Haskell2010
 
 test-suite smp-server-test
@@ -297,5 +297,5 @@ test-suite smp-server-test
     , x509-store ==1.6.*
     , x509-validation ==1.6.*
   if flag(swift)
-    ghc-options: -DswiftJSON
+    cpp-options: -DswiftJSON
   default-language: Haskell2010