diff --git a/src/config.h b/src/config.h
index 512fe40..68ae258 100644
--- a/src/config.h
+++ b/src/config.h
@@ -151,30 +151,6 @@
 */
 #define DEBUG_LEVEL DEBUG_C_REVISION
 
-/* CPU_SPIN_SHUTDN
-   If this symbol is defined, the cpu module implements the SHUTDN
-   instruction as a spin loop; when the instruction is encountered in the
-   run stream, the program counter is reset to the starting nibble of its
-   opcode.
-
-   If this symbol is not defined, the cpu module implements the SHUTDN
-   instruction signaling a Chf condition; the main emulator loop
-   condition handler works in concert with the GUI module to implement
-   an idle loop when this condition is handled.
-
-   This option MUST be defined if the revision of either the cpu emulation
-   module (cpu.c) or the GUI module (x11.c) is less than 3.1.
-
-   Starting from release 3.1, this option is disabled by default, to
-   waste as little (real) cpu time as possible; however, expect a
-   loss of timing accuracy.
-
-   Notice also that when this function is defined the CpuHaltRequest()
-   and CpuRunRequest() functions are disabled; as a consequence, all
-   interactive emulator's extended functions will be disabled as well.
-*/
-/* #define CPU_SPIN_SHUTDN */
-
 /* 2.1: FORCE_NONMODAL
    If this symbol is defined, nonmodal navigation is forced in the
    OSF/Motif GUI, by setting navigationType to XmNONE and traversalOn
diff --git a/src/cpu.c b/src/cpu.c
index a79df1f..135f827 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -362,24 +362,12 @@ static void ExecSHUTDN( void )
 {
     debug1( DEBUG_C_TRACE, CPU_I_CALLED, "SHUTDN" );
 
-#ifdef CPU_SPIN_SHUTDN
-    /* If the CPU_SPIN_SHUTDN symbol is defined, the CPU module implements
-       SHUTDN as a spin loop; the program counter is reset to the starting
-       nibble of the SHUTDN opcode.
-    */
-    cpu_status.PC -= 3;
-#endif
-
     /* Set shutdown flag */
     cpu_status.shutdn = 1;
 
-#ifndef CPU_SPIN_SHUTDN
-    /* If the CPU_SPIN_SHUTDN symbol is not defined, the CPU module implements
-       SHUTDN signalling the condition CPU_I_SHUTDN
-    */
+    /* the CPU module implements SHUTDN signalling the condition CPU_I_SHUTDN */
     ChfCondition CPU_I_SHUTDN, CHF_INFO ChfEnd;
     ChfSignal();
-#endif
 }
 
 /*---------------------------------------------------------------------------
@@ -2700,11 +2688,6 @@ void CpuWake( void )
             /* Clear SHUTDN flag */
             cpu_status.shutdn = 0;
 
-#ifdef CPU_SPIN_SHUTDN
-            /* Adjust PC if SHUTDN is implemented using a spin loop */
-            cpu_status.PC += 3;
-#endif
-
             /* Clear PC if necessary */
             /* if(cpu_status.OUT == (OutputRegister)0)
                  cpu_status.PC = (Address)0;
@@ -2768,12 +2751,6 @@ int CpuHaltRequest( void )
 {
     debug1( DEBUG_C_TRACE | DEBUG_C_INT, CPU_I_CALLED, "CpuHaltRequest" );
 
-#ifdef CPU_SPIN_SHUTDN
-    ChfCondition CPU_E_NO_HALT, CHF_ERROR ChfEnd;
-    ChfSignal();
-    return -1;
-
-#else
     if ( cpu_status.halt++ == 0 ) {
         debug0( DEBUG_C_INT, CPU_I_HALT );
 
@@ -2786,8 +2763,6 @@ int CpuHaltRequest( void )
     }
 
     return cpu_status.halt;
-
-#endif
 }
 
 /* .+
@@ -2822,12 +2797,6 @@ int CpuRunRequest( void )
 {
     debug1( DEBUG_C_TRACE | DEBUG_C_INT, CPU_I_CALLED, "CpuRunRequest" );
 
-#ifdef CPU_SPIN_SHUTDN
-    ChfCondition CPU_E_NO_HALT, CHF_ERROR ChfEnd;
-    ChfSignal();
-    return -1;
-
-#else
     if ( cpu_status.halt > 0 )
         if ( --cpu_status.halt == 0 ) {
             debug0( DEBUG_C_INT, CPU_I_RUN );
@@ -2837,8 +2806,6 @@ int CpuRunRequest( void )
         }
 
     return cpu_status.halt;
-
-#endif
 }
 
 /* .+
@@ -2866,13 +2833,7 @@ int CpuHaltAllowed( void )
 {
     debug1( DEBUG_C_TRACE | DEBUG_C_INT, CPU_I_CALLED, "CpuHaltAllowed" );
 
-#ifdef CPU_SPIN_SHUTDN
-    return 0;
-
-#else
     return 1;
-
-#endif
 }
 
 /* .+
diff --git a/src/emulator.c b/src/emulator.c
index 96ab2cf..cbec151 100644
--- a/src/emulator.c
+++ b/src/emulator.c
@@ -281,15 +281,6 @@ static ChfAction EmulatorLoopHandler( const ChfDescriptor* d, const ChfState s,
                 /* Condition from CPU modules; check Condition Code */
                 switch ( ChfGetConditionCode( d ) ) {
                     case CPU_I_SHUTDN:
-#ifdef CPU_SPIN_SHUTDN
-                        /* CPU shutdown signalled with CPU_SPIN_SHUTDN defined;
-                           Fatal error.
-                        */
-                        ChfCondition CPU_F_BAD_SHUTDN, CHF_FATAL ChfEnd;
-                        ChfSignal();
-
-                        act = CHF_RESIGNAL;
-#else
                         {
                             /* 3.1: CPU_SPIN_SHUTDN is not defined, and the cpu emulator
                                has just executed a shutdown instruction.
@@ -464,7 +455,6 @@ static ChfAction EmulatorLoopHandler( const ChfDescriptor* d, const ChfState s,
 
                             act = CHF_CONTINUE;
                         }
-#endif
                         break;
 
                     case CPU_I_EMULATOR_INT: