diff --git a/lighter/signer_client.py b/lighter/signer_client.py
index c1bb252..2364c56 100644
--- a/lighter/signer_client.py
+++ b/lighter/signer_client.py
@@ -29,7 +29,7 @@ class ApiKeyResponse(ctypes.Structure):
 
 class CreateOrderTxReq(ctypes.Structure):
     _fields_ = [
-        ("MarketIndex", ctypes.c_uint8),
+        ("MarketIndex", ctypes.c_int16),
         ("ClientOrderIndex", ctypes.c_longlong),
         ("BaseAmount", ctypes.c_longlong),
         ("Price", ctypes.c_uint32),
diff --git a/lighter/signers/lighter-signer-darwin-arm64.h b/lighter/signers/lighter-signer-darwin-arm64.h
index 307323c..e2f9e86 100644
--- a/lighter/signers/lighter-signer-darwin-arm64.h
+++ b/lighter/signers/lighter-signer-darwin-arm64.h
@@ -43,7 +43,7 @@ typedef struct {
 } ApiKeyResponse;
 
 typedef struct {
-    uint8_t MarketIndex;
+    int16_t MarketIndex;
     int64_t ClientOrderIndex;
     int64_t BaseAmount;
     uint32_t Price;
diff --git a/lighter/signers/lighter-signer-linux-amd64.h b/lighter/signers/lighter-signer-linux-amd64.h
index b097024..2b3ae4b 100644
--- a/lighter/signers/lighter-signer-linux-amd64.h
+++ b/lighter/signers/lighter-signer-linux-amd64.h
@@ -43,7 +43,7 @@ typedef struct {
 } ApiKeyResponse;
 
 typedef struct {
-    uint8_t MarketIndex;
+    int16_t MarketIndex;
     int64_t ClientOrderIndex;
     int64_t BaseAmount;
     uint32_t Price;
diff --git a/lighter/signers/lighter-signer-linux-arm64.h b/lighter/signers/lighter-signer-linux-arm64.h
index b097024..2b3ae4b 100644
--- a/lighter/signers/lighter-signer-linux-arm64.h
+++ b/lighter/signers/lighter-signer-linux-arm64.h
@@ -43,7 +43,7 @@ typedef struct {
 } ApiKeyResponse;
 
 typedef struct {
-    uint8_t MarketIndex;
+    int16_t MarketIndex;
     int64_t ClientOrderIndex;
     int64_t BaseAmount;
     uint32_t Price;
diff --git a/lighter/signers/lighter-signer-windows-amd64.h b/lighter/signers/lighter-signer-windows-amd64.h
index 164e01c..44a69af 100644
--- a/lighter/signers/lighter-signer-windows-amd64.h
+++ b/lighter/signers/lighter-signer-windows-amd64.h
@@ -43,7 +43,7 @@ typedef struct {
 } ApiKeyResponse;
 
 typedef struct {
-    uint8_t MarketIndex;
+    int16_t MarketIndex;
     int64_t ClientOrderIndex;
     int64_t BaseAmount;
     uint32_t Price;