diff --git a/libsrc/sim6502/paravirt.s b/libsrc/sim6502/paravirt.s
index 3bd40fbe4..b9fc38de5 100644
--- a/libsrc/sim6502/paravirt.s
+++ b/libsrc/sim6502/paravirt.s
@@ -7,9 +7,10 @@
 ; int __fastcall__ write (int fd, const void* buf, unsigned count);
 ;
 
-        .export         exit, args, _open, _close, _read, _write
+        .export         exit, args, _open, _close, _read, _write, _lseek
         .export         __sysremove, ___osmaperrno
 
+_lseek          := $FFF1
 __sysremove     := $FFF2
 ___osmaperrno   := $FFF3
 _open           := $FFF4
diff --git a/src/sim65/paravirt.c b/src/sim65/paravirt.c
index 141bcd2bd..4e68a3f0e 100644
--- a/src/sim65/paravirt.c
+++ b/src/sim65/paravirt.c
@@ -159,6 +159,30 @@ static void PVArgs (CPURegs* Regs)
     SetAX (Regs, ArgC);
 }
 
+/* Match between standard POSIX whence and cc65 whence. */
+static unsigned SEEK_MODE_MATCH[3] = {
+  SEEK_CUR,
+  SEEK_END,
+  SEEK_SET
+};
+
+static void PVLseek (CPURegs* Regs)
+{
+    unsigned RetVal;
+
+    unsigned Whence = GetAX (Regs);
+    unsigned Offset = PopParam (4);
+    unsigned FD     = PopParam (2);
+
+    Print (stderr, 2, "PVLseek ($%04X, $%08X, $%04X (%d))\n",
+           FD, Offset, Whence, SEEK_MODE_MATCH[Whence]);
+
+    RetVal = lseek(FD, (off_t)Offset, SEEK_MODE_MATCH[Whence]);
+    Print (stderr, 2, "PVLseek returned %04X\n", RetVal);
+
+    SetAX (Regs, RetVal);
+}
+
 
 
 static void PVOpen (CPURegs* Regs)
@@ -343,6 +367,7 @@ static void PVOSMapErrno (CPURegs* Regs)
 
 
 static const PVFunc Hooks[] = {
+    PVLseek,
     PVSysRemove,
     PVOSMapErrno,
     PVOpen,
diff --git a/src/sim65/paravirt.h b/src/sim65/paravirt.h
index f3281705e..109fdb847 100644
--- a/src/sim65/paravirt.h
+++ b/src/sim65/paravirt.h
@@ -44,7 +44,7 @@
 
 
 
-#define PARAVIRT_BASE        0xFFF2
+#define PARAVIRT_BASE        0xFFF1
 /* Lowest address used by a paravirtualization hook */
 
 #define PV_PATH_SIZE         1024
diff --git a/test/ref/test_fseek.c b/test/ref/test_fseek.c
new file mode 100644
index 000000000..e63dc0c02
--- /dev/null
+++ b/test/ref/test_fseek.c
@@ -0,0 +1,73 @@
+/*
+  !!DESCRIPTION!! fgets test
+  !!LICENCE!!     Public domain
+*/
+
+#include "common.h"
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+FILE *in;
+char bufA[32];
+char bufB[32];
+
+#define INFILE   "cf.in"
+
+int main(int argc,char **argv)
+{
+    static int r;
+
+    in = fopen(INFILE, "rb");
+    if (in == NULL) {
+        return EXIT_FAILURE;
+    }
+
+    r = fread(bufA, 1, sizeof(bufA), in);
+
+    if (r == 0) {
+      printf("Error: could not read.\n");
+      return EXIT_FAILURE;
+    }
+    fwrite(bufA, 1, r, stdout);
+
+    /* Test SEEK_SET */
+    fseek(in, 0, SEEK_SET);
+    r = fread(bufB, 1, sizeof(bufB), in);
+
+    if (r == 0) {
+      printf("Error: could not re-read after SEEK_SET.\n");
+      return EXIT_FAILURE;
+    }
+    fwrite(bufB, 1, r, stdout);
+
+    if (memcmp(bufA, bufB, sizeof(bufA))) {
+      printf("reads differ.\n");
+      return EXIT_FAILURE;
+    }
+
+    /* Test SEEK_CUR */
+    fseek(in, 0, SEEK_SET);
+    fseek(in, 1, SEEK_CUR);
+    r = fread(bufB, 1, sizeof(bufB), in);
+
+    if (r == 0) {
+      printf("Error: could not re-read after SEEK_CUR.\n");
+      return EXIT_FAILURE;
+    }
+    fwrite(bufB, 1, r, stdout);
+
+    if (memcmp(bufA+1, bufB, sizeof(bufA)-1)) {
+      printf("reads differ.\n");
+      return EXIT_FAILURE;
+    }
+
+
+    fclose(in);
+
+    return 0;
+}