diff --git a/bin/mbus-serial-request-data-multi-reply.c b/bin/mbus-serial-request-data-multi-reply.c
index 2213755..d0c06d1 100755
--- a/bin/mbus-serial-request-data-multi-reply.c
+++ b/bin/mbus-serial-request-data-multi-reply.c
@@ -121,7 +121,7 @@ main(int argc, char **argv)
         return 1;
     }
 
-    if (strlen(addr_str) == 16)
+    if (mbus_is_secondary_address(addr_str))
     {
         // secondary addressing
 
diff --git a/bin/mbus-serial-request-data.c b/bin/mbus-serial-request-data.c
index e4e22e1..74dacf3 100755
--- a/bin/mbus-serial-request-data.c
+++ b/bin/mbus-serial-request-data.c
@@ -88,7 +88,7 @@ main(int argc, char **argv)
     }
 
 
-    if (strlen(addr_str) == 16)
+    if (mbus_is_secondary_address(addr_str))
     {
         // secondary addressing
 
diff --git a/bin/mbus-serial-scan-secondary.c b/bin/mbus-serial-scan-secondary.c
index e85355e..b382f4a 100755
--- a/bin/mbus-serial-scan-secondary.c
+++ b/bin/mbus-serial-scan-secondary.c
@@ -128,7 +128,7 @@ main(int argc, char **argv)
         return 1;
     }
  
-    if (strlen(addr_mask) != 16)
+    if (mbus_is_secondary_address(addr_mask) == 0)
     {
         fprintf(stderr, "Misformatted secondary address mask. Must be 16 character HEX number.\n");
         free(addr_mask);
diff --git a/bin/mbus-serial-select-secondary.c b/bin/mbus-serial-select-secondary.c
index ad4a883..87f5b80 100755
--- a/bin/mbus-serial-select-secondary.c
+++ b/bin/mbus-serial-select-secondary.c
@@ -49,7 +49,7 @@ main(int argc, char **argv)
         return 1;
     }
  
-    if (strlen(addr) != 16)
+    if (mbus_is_secondary_address(addr) == 0)
     {
         printf("Misformatted secondary address. Must be 16 character HEX number.\n");
         return 1;
diff --git a/bin/mbus-tcp-raw-send.c b/bin/mbus-tcp-raw-send.c
index 8f58b97..7356573 100644
--- a/bin/mbus-tcp-raw-send.c
+++ b/bin/mbus-tcp-raw-send.c
@@ -90,7 +90,7 @@ main(int argc, char **argv)
         return 1;
     }
 
-    if (strlen(addr_str) == 16)
+    if (mbus_is_secondary_address(addr_str))
     {
         // secondary addressing
         int ret;
diff --git a/bin/mbus-tcp-request-data-multi-reply.c b/bin/mbus-tcp-request-data-multi-reply.c
index e682c1e..2b65c31 100755
--- a/bin/mbus-tcp-request-data-multi-reply.c
+++ b/bin/mbus-tcp-request-data-multi-reply.c
@@ -81,7 +81,7 @@ main(int argc, char **argv)
         return 1;
     }
 
-    if (strlen(addr_str) == 16)
+    if (mbus_is_secondary_address(addr_str))
     {
         // secondary addressing
 
diff --git a/bin/mbus-tcp-request-data.c b/bin/mbus-tcp-request-data.c
index 70aa4ee..07f72bf 100755
--- a/bin/mbus-tcp-request-data.c
+++ b/bin/mbus-tcp-request-data.c
@@ -70,7 +70,7 @@ main(int argc, char **argv)
         return 1;
     }
 
-    if (strlen(addr_str) == 16)
+    if (mbus_is_secondary_address(addr_str))
     {
         // secondary addressing
 
diff --git a/bin/mbus-tcp-scan-secondary.c b/bin/mbus-tcp-scan-secondary.c
index 761d86d..42d5565 100755
--- a/bin/mbus-tcp-scan-secondary.c
+++ b/bin/mbus-tcp-scan-secondary.c
@@ -53,7 +53,7 @@ main(int argc, char **argv)
         return 1;
     }
 
-    if (strlen(addr_mask) != 16)
+    if (mbus_is_secondary_address(addr_mask) == 0)
     {
         fprintf(stderr, "Misformatted secondary address mask. Must be 16 character HEX number.\n");
         return 1;
diff --git a/bin/mbus-tcp-select-secondary.c b/bin/mbus-tcp-select-secondary.c
index e894a97..904bd27 100755
--- a/bin/mbus-tcp-select-secondary.c
+++ b/bin/mbus-tcp-select-secondary.c
@@ -40,7 +40,7 @@ main(int argc, char **argv)
         return 1;
     }
 
-    if (strlen(addr) != 16)
+    if (mbus_is_secondary_address(addr) == 0)
     {
         printf("Misformatted secondary address. Must be 16 character HEX number.\n");
         return 1;
diff --git a/mbus/mbus-protocol-aux.c b/mbus/mbus-protocol-aux.c
index ed6df91..8340cbf 100755
--- a/mbus/mbus-protocol-aux.c
+++ b/mbus/mbus-protocol-aux.c
@@ -1629,6 +1629,12 @@ mbus_send_switch_baudrate_frame(mbus_handle * handle, int address, int baudrate)
     int control_information = 0;
     mbus_frame *frame;
     
+    if (mbus_is_primary_address(address) == 0)
+    {
+        MBUS_ERROR("%s: invalid address %d\n", __PRETTY_FUNCTION__, address);
+        return -1;
+    }
+    
     switch (baudrate)
     {
       case 300:
@@ -1690,6 +1696,12 @@ mbus_send_request_frame(mbus_handle * handle, int address)
 {
     int retval = 0;
     mbus_frame *frame;
+    
+    if (mbus_is_primary_address(address) == 0)
+    {
+        MBUS_ERROR("%s: invalid address %d\n", __PRETTY_FUNCTION__, address);
+        return -1;
+    }
 
     frame = mbus_frame_new(MBUS_FRAME_TYPE_SHORT);
     
@@ -1729,6 +1741,12 @@ mbus_sendrecv_request(mbus_handle *handle, int address, mbus_frame *reply, int m
         MBUS_ERROR("%s: Invalid M-Bus handle for request.\n", __PRETTY_FUNCTION__);
         return 1;
     }
+    
+    if (mbus_is_primary_address(address) == 0)
+    {
+        MBUS_ERROR("%s: invalid address %d\n", __PRETTY_FUNCTION__, address);
+        return 1;
+    }
 
     frame = mbus_frame_new(MBUS_FRAME_TYPE_SHORT);
     
@@ -1880,6 +1898,12 @@ mbus_send_ping_frame(mbus_handle *handle, int address, char purge_response)
 {
     int retval = 0;
     mbus_frame *frame;
+    
+    if (mbus_is_primary_address(address) == 0)
+    {
+        MBUS_ERROR("%s: invalid address %d\n", __PRETTY_FUNCTION__, address);
+        return 1;
+    }
         
     frame = mbus_frame_new(MBUS_FRAME_TYPE_SHORT);
     
diff --git a/mbus/mbus-protocol.c b/mbus/mbus-protocol.c
index 44d56dd..106c217 100755
--- a/mbus/mbus-protocol.c
+++ b/mbus/mbus-protocol.c
@@ -3957,9 +3957,15 @@ mbus_frame_select_secondary_pack(mbus_frame *frame, char *address)
     int val, i, j, k;
     char tmp[16];
 
-    if (frame == NULL || address == NULL || strlen(address) != 16)
+    if (frame == NULL || address == NULL)
     {
-        snprintf(error_str, sizeof(error_str), "%s: frame or address arguments are NULL or invalid.", __PRETTY_FUNCTION__);
+        snprintf(error_str, sizeof(error_str), "%s: frame or address arguments are NULL.", __PRETTY_FUNCTION__);
+        return -1;
+    }
+    
+    if (mbus_is_secondary_address(address) == 0)
+    {
+        snprintf(error_str, sizeof(error_str), "%s: address is invalid.", __PRETTY_FUNCTION__);
         return -1;
     }
 
@@ -4011,3 +4017,35 @@ mbus_frame_select_secondary_pack(mbus_frame *frame, char *address)
 
     return 0;
 }
+
+//---------------------------------------------------------
+// Checks if an integer is a valid primary address.
+//---------------------------------------------------------
+int
+mbus_is_primary_address(int value)
+{
+    return ((value >= 0x00) && (value <= 0xFF));
+}
+
+//---------------------------------------------------------
+// Checks if an string is a valid secondary address.
+//---------------------------------------------------------
+int
+mbus_is_secondary_address(const char * value)
+{
+    int i;
+    
+    if (value == NULL)
+        return 0;
+        
+    if (strlen(value) != 16)
+        return 0;
+        
+    for (i = 0; i < 16; i++)
+    {
+        if (!isxdigit(value[i]))
+            return 0;
+    }
+    
+    return 1;
+}
diff --git a/mbus/mbus-protocol.h b/mbus/mbus-protocol.h
index bd6192f..7eb8ecf 100755
--- a/mbus/mbus-protocol.h
+++ b/mbus/mbus-protocol.h
@@ -636,6 +636,9 @@ u_char mbus_dif_datalength_lookup(u_char dif);
 char *mbus_frame_get_secondary_address(mbus_frame *frame);
 int   mbus_frame_select_secondary_pack(mbus_frame *frame, char *address);
 
+int mbus_is_primary_address(int value);
+int mbus_is_secondary_address(const char * value);
+
 #ifdef __cplusplus
 }
 #endif