diff --git a/include/geos/gsys.h b/include/geos/gsys.h
index b60c9884b..1753492e5 100644
--- a/include/geos/gsys.h
+++ b/include/geos/gsys.h
@@ -35,7 +35,9 @@ char get_ostype(void);
 #define GATEWAY         0x08
 #define GEOS_V10        0x10
 #define GEOS_V11        0x11
-#define GEOS_V12        0x12    /* ??? not sure */
+#define GEOS_V12        0x12
+#define GEOS_V13        0x13
+#define GEOS_V15        0x15
 #define GEOS_V20        0x20
 #define WHEELS          0x40    /* only Wheels? */
 
diff --git a/libsrc/geos-cbm/system/get_ostype.s b/libsrc/geos-cbm/system/get_ostype.s
index 827630f0b..6e6731952 100644
--- a/libsrc/geos-cbm/system/get_ostype.s
+++ b/libsrc/geos-cbm/system/get_ostype.s
@@ -26,6 +26,8 @@ _get_ostype:
         and #%11110000
         cmp #$10
         beq geos10
+        cmp #$13                ; either 1.3 or 1.5
+        beq geos13check
         lda gatewayFlag
         cmp #$41
         beq gateway
@@ -37,6 +39,7 @@ _get_ostype:
         beq geos_on_plus4
         ora version
         rts
+geos13:
 geos10:
         lda version
         rts
@@ -54,6 +57,13 @@ megapatch3:
         lda #$03
         ora c128Flag
         rts
+geos13check:
+        lda mp3Flag
+        cmp #$03
+        bne geos13
+geos15:
+        lda #$15
+        rts
 
 _get_tv:
         jsr _get_ostype
diff --git a/samples/geos/geosver.c b/samples/geos/geosver.c
index 77a15ada7..1402d148e 100644
--- a/samples/geos/geosver.c
+++ b/samples/geos/geosver.c
@@ -32,6 +32,10 @@ void main (void)
             version = "GEOS v1.1";
         } else if (os == GEOS_V12) {
             version = "GEOS v1.2";
+        } else if (os == GEOS_V13) {
+            version = "GEOS v1.3";
+        } else if (os == GEOS_V15) {
+            version = "GEOS v1.5";
         } else if (os == GEOS_V20) {
             version = "GEOS v2.0";
         } else if (os == MEGAPATCH3) {