diff --git a/liteeth/phy/usp_gth_1000basex.py b/liteeth/phy/usp_gth_1000basex.py
index 4c89eb0..cb62223 100644
--- a/liteeth/phy/usp_gth_1000basex.py
+++ b/liteeth/phy/usp_gth_1000basex.py
@@ -556,7 +556,7 @@ class USP_GTH_1000BASEX(LiteXModule):
             i_CPLLLOCKDETCLK      = 0b0,
             i_CPLLLOCKEN          = 0b1,
             i_CPLLPD              = pll_reset,
-            i_CPLLREFCLKSEL       = 0b111,
+            i_CPLLREFCLKSEL       = 0b001,
             i_CPLLRESET           = 0b0,
             i_DMONFIFORESET       = 0b0,
             i_DMONITORCLK         = 0b0,
diff --git a/liteeth/phy/usp_gty_1000basex.py b/liteeth/phy/usp_gty_1000basex.py
index 00f5230..1465965 100644
--- a/liteeth/phy/usp_gty_1000basex.py
+++ b/liteeth/phy/usp_gty_1000basex.py
@@ -574,7 +574,7 @@ class USP_GTY_1000BASEX(LiteXModule):
             i_CPLLLOCKDETCLK      = 0b0,
             i_CPLLLOCKEN          = 0b1,
             i_CPLLPD              = pll_reset,
-            i_CPLLREFCLKSEL       = 0b111,
+            i_CPLLREFCLKSEL       = 0b001,
             i_CPLLRESET           = 0b0,
             i_DMONFIFORESET       = 0b0,
             i_DMONITORCLK         = 0b0,