diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index a719e54923..3b3b40fa73 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -158,22 +158,23 @@ zio_init(void)
 	zio_link_cache = kmem_cache_create("zio_link_cache",
 	    sizeof (zio_link_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
 
+	/*
+	 * For small buffers, we want a cache for each multiple of
+	 * SPA_MINBLOCKSIZE.  For larger buffers, we want a cache
+	 * for each quarter-power of 2.
+	 */
 	for (c = 0; c < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; c++) {
 		size_t size = (c + 1) << SPA_MINBLOCKSHIFT;
-		size_t align, cflags, data_cflags;
-		char name[32];
-
-		/*
-		 * Create cache for each half-power of 2 size, starting from
-		 * SPA_MINBLOCKSIZE.  It should give us memory space efficiency
-		 * of ~7/8, sufficient for transient allocations mostly using
-		 * these caches.
-		 */
 		size_t p2 = size;
+		size_t align = 0;
+		size_t data_cflags, cflags;
+
+		data_cflags = KMC_NODEBUG;
+		cflags = (zio_exclude_metadata || size > zio_buf_debug_limit) ?
+		    KMC_NODEBUG : 0;
+
 		while (!ISP2(p2))
 			p2 &= p2 - 1;
-		if (!IS_P2ALIGNED(size, p2 / 2))
-			continue;
 
 #ifndef _KERNEL
 		/*
@@ -184,37 +185,47 @@ zio_init(void)
 		 */
 		if (arc_watch && !IS_P2ALIGNED(size, PAGESIZE))
 			continue;
+		/*
+		 * Here's the problem - on 4K native devices in userland on
+		 * Linux using O_DIRECT, buffers must be 4K aligned or I/O
+		 * will fail with EINVAL, causing zdb (and others) to coredump.
+		 * Since userland probably doesn't need optimized buffer caches,
+		 * we just force 4K alignment on everything.
+		 */
+		align = 8 * SPA_MINBLOCKSIZE;
+#else
+		if (size < PAGESIZE) {
+			align = SPA_MINBLOCKSIZE;
+		} else if (IS_P2ALIGNED(size, p2 >> 2)) {
+			align = PAGESIZE;
+		}
 #endif
 
-		if (IS_P2ALIGNED(size, PAGESIZE))
-			align = PAGESIZE;
-		else
-			align = 1 << (highbit64(size ^ (size - 1)) - 1);
+		if (align != 0) {
+			char name[36];
+			if (cflags == data_cflags) {
+				/*
+				 * Resulting kmem caches would be identical.
+				 * Save memory by creating only one.
+				 */
+				(void) snprintf(name, sizeof (name),
+				    "zio_buf_comb_%lu", (ulong_t)size);
+				zio_buf_cache[c] = kmem_cache_create(name,
+				    size, align, NULL, NULL, NULL, NULL, NULL,
+				    cflags);
+				zio_data_buf_cache[c] = zio_buf_cache[c];
+				continue;
+			}
+			(void) snprintf(name, sizeof (name), "zio_buf_%lu",
+			    (ulong_t)size);
+			zio_buf_cache[c] = kmem_cache_create(name, size,
+			    align, NULL, NULL, NULL, NULL, NULL, cflags);
 
-		cflags = (zio_exclude_metadata || size > zio_buf_debug_limit) ?
-		    KMC_NODEBUG : 0;
-		data_cflags = KMC_NODEBUG;
-		if (cflags == data_cflags) {
-			/*
-			 * Resulting kmem caches would be identical.
-			 * Save memory by creating only one.
-			 */
-			(void) snprintf(name, sizeof (name),
-			    "zio_buf_comb_%lu", (ulong_t)size);
-			zio_buf_cache[c] = kmem_cache_create(name, size, align,
-			    NULL, NULL, NULL, NULL, NULL, cflags);
-			zio_data_buf_cache[c] = zio_buf_cache[c];
-			continue;
+			(void) snprintf(name, sizeof (name), "zio_data_buf_%lu",
+			    (ulong_t)size);
+			zio_data_buf_cache[c] = kmem_cache_create(name, size,
+			    align, NULL, NULL, NULL, NULL, NULL, data_cflags);
 		}
-		(void) snprintf(name, sizeof (name), "zio_buf_%lu",
-		    (ulong_t)size);
-		zio_buf_cache[c] = kmem_cache_create(name, size, align,
-		    NULL, NULL, NULL, NULL, NULL, cflags);
-
-		(void) snprintf(name, sizeof (name), "zio_data_buf_%lu",
-		    (ulong_t)size);
-		zio_data_buf_cache[c] = kmem_cache_create(name, size, align,
-		    NULL, NULL, NULL, NULL, NULL, data_cflags);
 	}
 
 	while (--c != 0) {