diff --git a/kmod/src/alloc.c b/kmod/src/alloc.c
index 34ebb4b5..392558ef 100644
--- a/kmod/src/alloc.c
+++ b/kmod/src/alloc.c
@@ -252,6 +252,7 @@ static struct scoutfs_ext_ops alloc_ext_ops = {
 	.next = alloc_ext_next,
 	.insert = alloc_ext_insert,
 	.remove = alloc_ext_remove,
+	.insert_overlap_warn = true,
 };
 
 static bool invalid_extent(u64 start, u64 end, u64 first, u64 last)
diff --git a/kmod/src/ext.c b/kmod/src/ext.c
index fdb1198a..b41ba043 100644
--- a/kmod/src/ext.c
+++ b/kmod/src/ext.c
@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/fs.h>
 
+#include "msg.h"
 #include "ext.h"
 #include "counters.h"
 #include "scoutfs_trace.h"
@@ -191,6 +192,9 @@ int scoutfs_ext_insert(struct super_block *sb, struct scoutfs_ext_ops *ops,
 
 	/* inserting extent must not overlap */
 	if (found.len && ext_overlap(&ins, found.start, found.len)) {
+		if (ops->insert_overlap_warn)
+			scoutfs_err(sb, "inserting extent %llu.%llu overlaps existing %llu.%llu",
+					start, len, found.start, found.len);
 		ret = -EINVAL;
 		goto out;
 	}
@@ -242,6 +246,8 @@ int scoutfs_ext_remove(struct super_block *sb, struct scoutfs_ext_ops *ops,
 
 	/* removed extent must be entirely within found */
 	if (!scoutfs_ext_inside(start, len, &found)) {
+		scoutfs_err(sb, "error removing extent %llu.%llu, isn't inside existing %llu.%llu",
+				start, len, found.start, found.len);
 		ret = -EINVAL;
 		goto out;
 	}
diff --git a/kmod/src/ext.h b/kmod/src/ext.h
index d826d21a..baf4e6d1 100644
--- a/kmod/src/ext.h
+++ b/kmod/src/ext.h
@@ -15,6 +15,8 @@ struct scoutfs_ext_ops {
 		      u64 start, u64 len, u64 map, u8 flags);
 	int (*remove)(struct super_block *sb, void *arg, u64 start, u64 len,
 		      u64 map, u8 flags);
+
+	bool insert_overlap_warn;
 };
 
 bool scoutfs_ext_can_merge(struct scoutfs_extent *left,