diff --git a/docs/api-reference.md b/docs/api-reference.md
index 6cb8209..4a830e2 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -18,6 +18,11 @@ usable either directly or transparently through `dmdevfs`/`/dev`.
 
 ## IOCTL commands (`dmfmc_ioctl_cmd_t`)
 
+Commands are numbered from `DMDRVI_IOCTL_CUSTOM_BASE` so they do not
+collide with the standard `DMDRVI_IOCTL_*` commands. Any command outside this
+range (e.g. the `DMDRVI_IOCTL_BLOCK_GET_INFO` / `DMDRVI_IOCTL_MONITOR_GET_POLICY`
+probes sent by dmdevfs) is answered with `-ENOTTY`.
+
 | Command | `arg` type | Meaning |
 |---------|-----------|---------|
 | `dmfmc_ioctl_cmd_get_memory_start` | `void **` | Direct pointer to the mapped memory. |
diff --git a/include/dmfmc_types.h b/include/dmfmc_types.h
index 78180d2..f5e6da4 100644
--- a/include/dmfmc_types.h
+++ b/include/dmfmc_types.h
@@ -2,6 +2,7 @@
 #define DMFMC_TYPES_H
 
 #include <stdint.h>
+#include "dmdrvi_ioctl.h"
 #include <stdbool.h>
 #include <stddef.h>
 
@@ -185,7 +186,10 @@ typedef enum
  */
 typedef enum
 {
-    dmfmc_ioctl_cmd_get_memory_start = 1,   /**< arg = void** - direct pointer to the mapped memory */
+    /* Private commands start at DMDRVI_IOCTL_CUSTOM_BASE (dmdrvi_ioctl.h)
+     * so they never collide with the standard DMDRVI_IOCTL_* commands (network,
+     * block, monitor) that dmdevfs and other generic clients send to any node. */
+    dmfmc_ioctl_cmd_get_memory_start = DMDRVI_IOCTL_CUSTOM_BASE, /**< arg = void** - direct pointer to the mapped memory */
     dmfmc_ioctl_cmd_get_memory_size,        /**< arg = uint32_t* - size in bytes of the mapped memory */
     dmfmc_ioctl_cmd_get_configured_frequency, /**< arg = uint32_t* - SDCLK frequency actually configured (Hz) */
     dmfmc_ioctl_cmd_get_heap_context,       /**< arg = dmheap_context_t** - heap context, or NULL if not used as heap */
diff --git a/src/dmfmc.c b/src/dmfmc.c
index c5fdb25..3d656a2 100644
--- a/src/dmfmc.c
+++ b/src/dmfmc.c
@@ -503,10 +503,12 @@ dmod_dmdrvi_dif_api_declaration(2.0, dmfmc, int, _ioctl, ( dmdrvi_context_t cont
         return -EINVAL;
     }
 
-    if (command >= dmfmc_ioctl_cmd_max)
+    /* Not an error: generic clients (e.g. dmdevfs probing every node for the
+     * block/monitor classes) send standard DMDRVI_IOCTL_* commands the FMC
+     * does not implement - answer -ENOTTY quietly, as dmdrvi expects. */
+    if (command < dmfmc_ioctl_cmd_get_memory_start || command >= dmfmc_ioctl_cmd_max)
     {
-        DMOD_LOG_ERROR("Invalid ioctl command %d\n", command);
-        return -EINVAL;
+        return -ENOTTY;
     }
 
     switch (command)
@@ -555,7 +557,7 @@ dmod_dmdrvi_dif_api_declaration(2.0, dmfmc, int, _ioctl, ( dmdrvi_context_t cont
             return configure(context);
 
         default:
-            return -EINVAL;
+            return -ENOTTY;
     }
 }
 
diff --git a/src/port/CMakeLists.txt b/src/port/CMakeLists.txt
index 671c696..f9dcdff 100644
--- a/src/port/CMakeLists.txt
+++ b/src/port/CMakeLists.txt
@@ -38,8 +38,10 @@ dmod_add_library(${DMOD_MODULE_NAME} ${DMOD_MODULE_VERSION}
     ${COMMON_SOURCES}
 )
 
+# dmdrvi: dmfmc_types.h pulls in dmdrvi_ioctl.h (DMDRVI_IOCTL_CUSTOM_BASE)
 dmod_link_modules(${DMOD_MODULE_NAME}
     dmclk_port
+    dmdrvi
 )
 
 target_include_directories(${DMOD_MODULE_NAME} BEFORE PRIVATE