diff --git a/cocotbext/axi/axi_master.py b/cocotbext/axi/axi_master.py
index c298035..d9cf729 100644
--- a/cocotbext/axi/axi_master.py
+++ b/cocotbext/axi/axi_master.py
@@ -282,6 +282,9 @@ class AxiMasterWrite(Reset):
         if address < 0 or address >= 2**self.address_width:
             raise ValueError("Address out of range")
 
+        if isinstance(data, int):
+            raise ValueError("Expected bytes or bytearray for data")
+
         if awid is None or awid < 0:
             awid = None
         elif awid > self.id_count:
diff --git a/cocotbext/axi/axil_master.py b/cocotbext/axi/axil_master.py
index b001963..2fbfa79 100644
--- a/cocotbext/axi/axil_master.py
+++ b/cocotbext/axi/axil_master.py
@@ -150,6 +150,9 @@ class AxiLiteMasterWrite(Reset):
         if address < 0 or address >= 2**self.address_width:
             raise ValueError("Address out of range")
 
+        if isinstance(data, int):
+            raise ValueError("Expected bytes or bytearray for data")
+
         if not self.awprot_present and prot != AxiProt.NONSECURE:
             raise ValueError("awprot sideband signal value specified, but signal is not connected")