diff --git a/src/i2c_software.c b/src/i2c_software.c
index 990948644..77da94471 100644
--- a/src/i2c_software.c
+++ b/src/i2c_software.c
@@ -26,12 +26,19 @@ command_i2c_set_software_bus(uint32_t *args)
 {
     struct i2cdev_s *i2c = i2cdev_oid_lookup(args[0]);
     struct i2c_software *is = alloc_chunk(sizeof(*is));
+    uint32_t rate = args[3];
     is->ticks = CONFIG_CLOCK_FREQ / (100000 * 2); // 100KHz
     is->addr = (args[4] & 0x7f) << 1; // address format shifted
     is->scl_in = gpio_in_setup(args[1], 1);
     is->scl_out = gpio_out_setup(args[1], 1);
     is->sda_in = gpio_in_setup(args[2], 1);
     is->sda_out = gpio_out_setup(args[2], 1);
+    while (rate > 100000) {
+        rate = rate >> 1;
+        if (rate < 100000)
+            break;
+        is->ticks = is->ticks >> 1;
+    }
     i2cdev_set_software_bus(i2c, is);
 }
 DECL_COMMAND(command_i2c_set_software_bus,