diff --git a/source/installer.c b/source/installer.c
index 152a599..cf1ac6a 100644
--- a/source/installer.c
+++ b/source/installer.c
@@ -132,6 +132,11 @@ u32 SafeB9SInstaller(void) {
         statusFirm = STATUS_RED;
         return 1;
     }
+    if (CheckBoot9Strap(FIRM_BUFFER) != 0) {
+        snprintf(msgFirm, 64, "not boot9strap");
+        statusFirm = STATUS_RED;
+        return 1;
+    }
     snprintf(msgFirm, 64, "loaded & verified");
     statusFirm = STATUS_GREEN;
     ShowInstallerStatus();
diff --git a/source/safety/validator.c b/source/safety/validator.c
index 5436e44..2a5f0bd 100644
--- a/source/safety/validator.c
+++ b/source/safety/validator.c
@@ -5,6 +5,9 @@
 #define FIRM_MAGIC  'F', 'I', 'R', 'M'
 #define FIRM_MAX_SIZE  0x400000 // 4MB, due to FIRM partition size
 
+#define B9S_MAGIC   "B9S"
+#define B9S_OFFSET  (0x40 - strnlen(B9S_MAGIC, 0x10))
+
 // see: https://www.3dbrew.org/wiki/FIRM#Firmware_Section_Headers
 typedef struct {
     u32 offset;
@@ -110,3 +113,7 @@ u32 CheckFirmSigHax(void* firm) {
     FirmHeader* header = (FirmHeader*) firm;
     return (sha_cmp(sighaxHash, header->signature, 0x100, SHA256_MODE) == 0) ? 0 : 1;
 }
+
+u32 CheckBoot9Strap(void* firm) {
+    return (memcmp(((u8*) firm) + B9S_OFFSET, B9S_MAGIC, strnlen(B9S_MAGIC, 0x10)) == 0) ? 0 : 1;
+}
diff --git a/source/safety/validator.h b/source/safety/validator.h
index e03adca..fb9225a 100644
--- a/source/safety/validator.h
+++ b/source/safety/validator.h
@@ -5,3 +5,4 @@
 u32 ValidateFirm(void* firm, u8* firm_sha, u32 firm_size, char* output);
 u32 ValidateSector(void* sector);
 u32 CheckFirmSigHax(void* firm);
+u32 CheckBoot9Strap(void* firm);