diff --git a/clientgui/sg_BoincSimpleFrame.cpp b/clientgui/sg_BoincSimpleFrame.cpp
index 5793ba36dd..c9c33e7d5d 100755
--- a/clientgui/sg_BoincSimpleFrame.cpp
+++ b/clientgui/sg_BoincSimpleFrame.cpp
@@ -1118,7 +1118,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMajor) returned error %ld\n", err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (major < toMajor) return -1;
     if (major > toMajor) return 1;
@@ -1126,7 +1126,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMinor) returned error %ld\n", err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (minor < toMinor) return -1;
     if (minor > toMinor) return 1;
diff --git a/clientscr/Mac_Saver_ModuleView.m b/clientscr/Mac_Saver_ModuleView.m
index 97f0085893..88880f5441 100644
--- a/clientscr/Mac_Saver_ModuleView.m
+++ b/clientscr/Mac_Saver_ModuleView.m
@@ -611,7 +611,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMajor) returned error %ld\n", (long)err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (major < toMajor) return -1;
     if (major > toMajor) return 1;
@@ -619,7 +619,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMinor) returned error %ld\n", (long)err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (minor < toMinor) return -1;
     if (minor > toMinor) return 1;
diff --git a/mac_installer/AddRemoveUser.cpp b/mac_installer/AddRemoveUser.cpp
index 4b0f6f7daf..25d52880bf 100644
--- a/mac_installer/AddRemoveUser.cpp
+++ b/mac_installer/AddRemoveUser.cpp
@@ -267,7 +267,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMajor) returned error %ld\n", err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (major < toMajor) return -1;
     if (major > toMajor) return 1;
@@ -275,7 +275,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMinor) returned error %ld\n", err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (minor < toMinor) return -1;
     if (minor > toMinor) return 1;
diff --git a/mac_installer/PostInstall.cpp b/mac_installer/PostInstall.cpp
index 3ba346c82d..0e05204d48 100644
--- a/mac_installer/PostInstall.cpp
+++ b/mac_installer/PostInstall.cpp
@@ -1772,7 +1772,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stdout, "Gestalt(gestaltSystemVersionMajor) returned error %ld\n", err);
         fflush(stdout);
-        exit(-1);
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (major < toMajor) return -1;
     if (major > toMajor) return 1;
@@ -1780,7 +1780,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stdout, "Gestalt(gestaltSystemVersionMinor) returned error %ld\n", err);
         fflush(stdout);
-        exit(-1);
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (minor < toMinor) return -1;
     if (minor > toMinor) return 1;
diff --git a/mac_installer/uninstall.cpp b/mac_installer/uninstall.cpp
index 2bb6760d3f..710db6d8e8 100644
--- a/mac_installer/uninstall.cpp
+++ b/mac_installer/uninstall.cpp
@@ -1603,7 +1603,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMajor) returned error %ld\n", err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (major < toMajor) return -1;
     if (major > toMajor) return 1;
@@ -1611,7 +1611,7 @@ static int compareOSVersionTo(int toMajor, int toMinor) {
     if (err != noErr) {
         fprintf(stderr, "Gestalt(gestaltSystemVersionMinor) returned error %ld\n", err);
         fflush(stderr);
-        return 0;
+        return -1;  // gestaltSystemVersionMajor selector was not available before OS 10.4
     }
     if (minor < toMinor) return -1;
     if (minor > toMinor) return 1;