diff --git a/src/math/iir_df1.c b/src/math/iir_df1.c
index 5e4d13b8cc70..6a2bde2f5ddd 100644
--- a/src/math/iir_df1.c
+++ b/src/math/iir_df1.c
@@ -21,8 +21,12 @@ int iir_delay_size_df1(struct sof_eq_iir_header *config)
 	if (!n || n > SOF_EQ_IIR_BIQUADS_MAX)
 		return -EINVAL;
 
+	/* The filter runs num_sections_in_series biquads per parallel
+	 * branch, so the sections must split evenly into branches.
+	 */
 	if (!config->num_sections_in_series ||
-	    config->num_sections_in_series > n)
+	    config->num_sections_in_series > n ||
+	    n % config->num_sections_in_series)
 		return -EINVAL;
 
 	return 4 * n * sizeof(int32_t);
diff --git a/src/math/iir_df2t.c b/src/math/iir_df2t.c
index ed2b50a21a4e..8eac5c26aa07 100644
--- a/src/math/iir_df2t.c
+++ b/src/math/iir_df2t.c
@@ -21,8 +21,12 @@ int iir_delay_size_df2t(struct sof_eq_iir_header *config)
 	if (!n || n > SOF_EQ_IIR_BIQUADS_MAX)
 		return -EINVAL;
 
+	/* The filter runs num_sections_in_series biquads per parallel
+	 * branch, so the sections must split evenly into branches.
+	 */
 	if (!config->num_sections_in_series ||
-	    config->num_sections_in_series > n)
+	    config->num_sections_in_series > n ||
+	    n % config->num_sections_in_series)
 		return -EINVAL;
 
 	return 2 * n * sizeof(int64_t);
diff --git a/test/cmocka/src/audio/eq_iir/eq_iir_process.c b/test/cmocka/src/audio/eq_iir/eq_iir_process.c
index f69eaa39c129..6b30a64c5217 100644
--- a/test/cmocka/src/audio/eq_iir/eq_iir_process.c
+++ b/test/cmocka/src/audio/eq_iir/eq_iir_process.c
@@ -17,6 +17,8 @@
 #include <sof/audio/sink_api.h>
 #include <sof/audio/source_api.h>
 #include <ipc/control.h>
+#include <user/eq.h>
+#include <errno.h>
 
 #include "../../util.h"
 #include "../../../include/cmocka_chirp_2ch.h"
@@ -517,11 +519,29 @@ static struct test_parameters parameters[] = {
 
 };
 
+static void test_iir_delay_size_df1_series(void **state)
+{
+	struct sof_eq_iir_header hdr = { .num_sections = 11 };
+	const int size = 4 * 11 * sizeof(int32_t);
+
+	(void)state;
+
+	hdr.num_sections_in_series = 11;
+	assert_int_equal(iir_delay_size_df1(&hdr), size);
+
+	hdr.num_sections_in_series = 1;
+	assert_int_equal(iir_delay_size_df1(&hdr), size);
+
+	/* iir_df1() would run 20 biquads against 11 sections of state */
+	hdr.num_sections_in_series = 10;
+	assert_int_equal(iir_delay_size_df1(&hdr), -EINVAL);
+}
+
 int main(void)
 {
 	int i;
 
-	struct CMUnitTest tests[ARRAY_SIZE(parameters)];
+	struct CMUnitTest tests[ARRAY_SIZE(parameters) + 1];
 
 	for (i = 0; i < ARRAY_SIZE(parameters); i++) {
 		tests[i].name = "test_audio_eq_iir";
@@ -531,6 +551,12 @@ int main(void)
 		tests[i].initial_state = &parameters[i];
 	}
 
+	tests[i].name = "test_iir_delay_size_df1_series";
+	tests[i].test_func = test_iir_delay_size_df1_series;
+	tests[i].setup_func = NULL;
+	tests[i].teardown_func = NULL;
+	tests[i].initial_state = NULL;
+
 	cmocka_set_message_output(CM_OUTPUT_TAP);
 
 	return cmocka_run_group_tests(tests, setup_group, NULL);