diff --git a/include/acpi/acpigen.h b/include/acpi/acpigen.h
index 7365cce738..31366f5e34 100644
--- a/include/acpi/acpigen.h
+++ b/include/acpi/acpigen.h
@@ -65,4 +65,7 @@ void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size);
  */
 void acpigen_emit_string(struct acpi_ctx *ctx, const char *str);
 
+void acpigen_write_len_f(struct acpi_ctx *ctx);
+void acpigen_pop_len(struct acpi_ctx *ctx);
+
 #endif
diff --git a/include/dm/acpi.h b/include/dm/acpi.h
index 7563a4c60a..2bd03eaa0a 100644
--- a/include/dm/acpi.h
+++ b/include/dm/acpi.h
@@ -22,6 +22,9 @@
 /* Length of an ACPI name string including nul terminator */
 #define ACPI_NAME_MAX	(ACPI_NAME_LEN + 1)
 
+/* Number of nested objects supported */
+#define ACPIGEN_LENSTACK_SIZE 10
+
 #if !defined(__ACPI__)
 
 /**
@@ -34,12 +37,16 @@
  *	adding a new table. The RSDP holds pointers to the RSDT and XSDT.
  * @rsdt: Pointer to the Root System Description Table
  * @xsdt: Pointer to the Extended System Description Table
+ * @len_stack: Stack of 'length' words to fix up later
+ * @ltop: Points to current top of stack (0 = empty)
  */
 struct acpi_ctx {
 	void *current;
 	struct acpi_rsdp *rsdp;
 	struct acpi_rsdt *rsdt;
 	struct acpi_xsdt *xsdt;
+	char *len_stack[ACPIGEN_LENSTACK_SIZE];
+	int ltop;
 };
 
 /**
diff --git a/lib/acpi/acpigen.c b/lib/acpi/acpigen.c
index 1223f0d1c4..bd1fa24fb6 100644
--- a/lib/acpi/acpigen.c
+++ b/lib/acpi/acpigen.c
@@ -10,6 +10,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <log.h>
 #include <acpi/acpigen.h>
 #include <dm/acpi.h>
 
@@ -37,6 +38,38 @@ void acpigen_emit_dword(struct acpi_ctx *ctx, uint data)
 	acpigen_emit_byte(ctx, (data >> 24) & 0xff);
 }
 
+/*
+ * Maximum length for an ACPI object generated by this code,
+ *
+ * If you need to change this, change acpigen_write_len_f(ctx) and
+ * acpigen_pop_len(ctx)
+ */
+#define ACPIGEN_MAXLEN 0xfffff
+
+void acpigen_write_len_f(struct acpi_ctx *ctx)
+{
+	assert(ctx->ltop < (ACPIGEN_LENSTACK_SIZE - 1));
+	ctx->len_stack[ctx->ltop++] = ctx->current;
+	acpigen_emit_byte(ctx, 0);
+	acpigen_emit_byte(ctx, 0);
+	acpigen_emit_byte(ctx, 0);
+}
+
+void acpigen_pop_len(struct acpi_ctx *ctx)
+{
+	int len;
+	char *p;
+
+	assert(ctx->ltop > 0);
+	p = ctx->len_stack[--ctx->ltop];
+	len = ctx->current - (void *)p;
+	assert(len <= ACPIGEN_MAXLEN);
+	/* generate store length for 0xfffff max */
+	p[0] = (0x80 | (len & 0xf));
+	p[1] = (len >> 4 & 0xff);
+	p[2] = (len >> 12 & 0xff);
+}
+
 void acpigen_emit_stream(struct acpi_ctx *ctx, const char *data, int size)
 {
 	int i;
diff --git a/test/dm/acpigen.c b/test/dm/acpigen.c
index 3d580a23a5..f9c15b7503 100644
--- a/test/dm/acpigen.c
+++ b/test/dm/acpigen.c
@@ -22,7 +22,7 @@
 #define TEST_STRING	"frogmore"
 #define TEST_STREAM2	"\xfa\xde"
 
-static int alloc_context(struct acpi_ctx **ctxp)
+static int alloc_context_size(struct acpi_ctx **ctxp, int size)
 {
 	struct acpi_ctx *ctx;
 
@@ -30,7 +30,8 @@ static int alloc_context(struct acpi_ctx **ctxp)
 	ctx = malloc(sizeof(*ctx));
 	if (!ctx)
 		return -ENOMEM;
-	ctx->current = malloc(150);
+	ctx->current = malloc(size);
+	ctx->ltop = 0;
 	if (!ctx->current)
 		return -ENOMEM;
 	*ctxp = ctx;
@@ -38,6 +39,11 @@ static int alloc_context(struct acpi_ctx **ctxp)
 	return 0;
 }
 
+static int alloc_context(struct acpi_ctx **ctxp)
+{
+	return alloc_context_size(ctxp, 150);
+}
+
 static void free_context(struct acpi_ctx **ctxp)
 {
 	free(*ctxp);
@@ -334,3 +340,57 @@ static int dm_test_acpi_spi(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_acpi_spi, DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
+
+/**
+ * get_length() - decode a three-byte length field
+ *
+ * @ptr: Length encoded as per ACPI
+ * @return decoded length, or -EINVAL on error
+ */
+static int get_length(u8 *ptr)
+{
+	if (!(*ptr & 0x80))
+		return -EINVAL;
+
+	return (*ptr & 0xf) | ptr[1] << 4 | ptr[2] << 12;
+}
+
+/* Test emitting a length */
+static int dm_test_acpi_len(struct unit_test_state *uts)
+{
+	const int size = 0xc0000;
+	struct acpi_ctx *ctx;
+	u8 *ptr;
+	int i;
+
+	ut_assertok(alloc_context_size(&ctx, size));
+
+	ptr = acpigen_get_current(ctx);
+
+	/* Write a byte and a 3-byte length */
+	acpigen_write_len_f(ctx);
+	acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(1 + 3, get_length(ptr));
+
+	/* Write 200 bytes so we need two length bytes */
+	ptr = ctx->current;
+	acpigen_write_len_f(ctx);
+	for (i = 0; i < 200; i++)
+		acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(200 + 3, get_length(ptr));
+
+	/* Write 40KB so we need three length bytes */
+	ptr = ctx->current;
+	acpigen_write_len_f(ctx);
+	for (i = 0; i < 40000; i++)
+		acpigen_emit_byte(ctx, 0x23);
+	acpigen_pop_len(ctx);
+	ut_asserteq(40000 + 3, get_length(ptr));
+
+	free_context(&ctx);
+
+	return 0;
+}
+DM_TEST(dm_test_acpi_len, 0);
