diff --git a/src/cocoa/app.mm b/src/cocoa/app.mm
index 6a2c443ac4..6222f501b5 100644
--- a/src/cocoa/app.mm
+++ b/src/cocoa/app.mm
@@ -174,10 +174,11 @@ bool wxApp::Initialize(int& argc, wxChar **argv)
     if ( argc > 1 )
     {
         static const wxChar *ARG_PSN = _T("-psn_");
-        if ( wxStrncmp(argv[1], ARG_PSN, sizeof(ARG_PSN) - 1) == 0 )
+        if ( wxStrncmp(argv[1], ARG_PSN, strlen(ARG_PSN)) == 0 )
         {
             // remove this argument
-            memmove(argv, argv + 1, argc--);
+            --argc;
+            memmove(argv + 1, argv + 2, argc * sizeof(char *));
         }
     }
 
diff --git a/src/mac/app.cpp b/src/mac/app.cpp
index a8ca3cdb66..57a0a7a787 100644
--- a/src/mac/app.cpp
+++ b/src/mac/app.cpp
@@ -609,10 +609,11 @@ bool wxApp::Initialize(int& argc, wxChar **argv)
     if ( argc > 1 )
     {
         static const wxChar *ARG_PSN = _T("-psn_");
-        if ( wxStrncmp(argv[1], ARG_PSN, sizeof(ARG_PSN) - 1) == 0 )
+        if ( wxStrncmp(argv[1], ARG_PSN, strlen(ARG_PSN)) == 0 )
         {
             // remove this argument
-            memmove(argv, argv + 1, argc--);
+            --argc;
+            memmove(argv + 1, argv + 2, argc * sizeof(char *));
         }
     }
 
diff --git a/src/mac/carbon/app.cpp b/src/mac/carbon/app.cpp
index a8ca3cdb66..57a0a7a787 100644
--- a/src/mac/carbon/app.cpp
+++ b/src/mac/carbon/app.cpp
@@ -609,10 +609,11 @@ bool wxApp::Initialize(int& argc, wxChar **argv)
     if ( argc > 1 )
     {
         static const wxChar *ARG_PSN = _T("-psn_");
-        if ( wxStrncmp(argv[1], ARG_PSN, sizeof(ARG_PSN) - 1) == 0 )
+        if ( wxStrncmp(argv[1], ARG_PSN, strlen(ARG_PSN)) == 0 )
         {
             // remove this argument
-            memmove(argv, argv + 1, argc--);
+            --argc;
+            memmove(argv + 1, argv + 2, argc * sizeof(char *));
         }
     }