diff --git a/firmware/target/arm/as3525/debug-as3525.c b/firmware/target/arm/as3525/debug-as3525.c
index 5c135cc10d..9f7b46df8e 100644
--- a/firmware/target/arm/as3525/debug-as3525.c
+++ b/firmware/target/arm/as3525/debug-as3525.c
@@ -143,12 +143,11 @@ static int calc_freq(int clk)
                     return 0;
             }
         case CLK_EXTMEM:
-        /* bits 1:0 of CGU_PERI always read as 0 and we assume source = PLLA */
 #if CONFIG_CPU == AS3525
             switch(CGU_PERI & 3) {
 #else
-        /* bits 1:0 of CGU_PERI always read as 0 and we assume source = PLLA */
-            switch(1) {
+            /* bits 1:0 of CGU_PERI always read as 0 and source = FCLK */
+            switch(3) {
 #endif
                 case 0:
                     return CLK_MAIN/(((CGU_PERI>>2)& 0xf)+1);