diff --git a/src/arch/riscv/core/zicntr.c b/src/arch/riscv/core/zicntr.c
index 7ea9f96ad..fb632b8c0 100644
--- a/src/arch/riscv/core/zicntr.c
+++ b/src/arch/riscv/core/zicntr.c
@@ -32,7 +32,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <string.h>
 #include <errno.h>
 #include <ipxe/fdt.h>
-#include <ipxe/hart.h>
+#include <ipxe/csr.h>
 #include <ipxe/timer.h>
 
 /** Timer increment per microsecond */
@@ -145,10 +145,10 @@ static int zicntr_probe ( void ) {
 	} u;
 	int rc;
 
-	/* Check if Zicntr extension is supported */
-	if ( ( rc = hart_supported ( "_zicntr" ) ) != 0 ) {
-		DBGC ( colour, "ZICNTR not supported: %s\n", strerror ( rc ) );
-		return rc;
+	/* Check if time CSR can be read */
+	if ( ! csr_can_read ( "time" ) ) {
+		DBGC ( colour, "ZICNTR cannot read TIME CSR\n" );
+		return -ENOTSUP;
 	}
 
 	/* Get timer frequency */
diff --git a/src/arch/riscv/core/zkr.c b/src/arch/riscv/core/zkr.c
index 4b6316ea0..b27a7f076 100644
--- a/src/arch/riscv/core/zkr.c
+++ b/src/arch/riscv/core/zkr.c
@@ -30,7 +30,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  */
 
 #include <errno.h>
-#include <ipxe/hart.h>
 #include <ipxe/csr.h>
 #include <ipxe/entropy.h>
 #include <ipxe/drbg.h>
@@ -53,13 +52,6 @@ struct entropy_source zkr_entropy __entropy_source ( ENTROPY_PREFERRED );
  * @ret rc		Return status code
  */
 static int zkr_entropy_enable ( void ) {
-	int rc;
-
-	/* Check if Zkr extension is supported */
-	if ( ( rc = hart_supported ( "_zkr" ) ) != 0 ) {
-		DBGC ( colour, "ZKR not supported: %s\n", strerror ( rc ) );
-		return rc;
-	}
 
 	/* Check if seed CSR is accessible in S-mode */
 	if ( ! csr_can_write ( "seed", 0 ) ) {