diff --git a/src/include/ngspice/sharedspice.h b/src/include/ngspice/sharedspice.h
index 00c2eabbf..f5c8ff0bf 100644
--- a/src/include/ngspice/sharedspice.h
+++ b/src/include/ngspice/sharedspice.h
@@ -86,6 +86,8 @@ Memory allocated in the calling program has to be freed only there.
 ngspice.dll should never call exit() directly, but handle either the 'quit'
 request to the caller or an request for exiting upon error,
 done by callback function ngexit().
+
+All boolean signals (BOOL) are of type int.
 */
 
 #ifndef NGSPICE_PACKAGE_VERSION
@@ -128,6 +130,9 @@ struct ngcomplex {
 typedef struct ngcomplex ngcomplex_t;
 #endif
 
+/* For C++ compatibility */
+typedef int BOOL;
+
 /* vector info obtained from any vector in ngspice.dll.
    Allows direct access to the ngspice internal vector structure,
    as defined in include/ngspice/devc.h . */
@@ -144,8 +149,8 @@ typedef struct vecvalues {
     char* name;        /* name of a specific vector */
     double creal;      /* actual data value */
     double cimag;      /* actual data value */
-    bool is_scale;     /* if 'name' is the scale vector */
-    bool is_complex;   /* if the data are complex numbers */
+    BOOL is_scale;     /* if 'name' is the scale vector */
+    BOOL is_complex;   /* if the data are complex numbers */
 } vecvalues, *pvecvalues;
 
 typedef struct vecvaluesall {
@@ -159,7 +164,7 @@ typedef struct vecinfo
 {
     int number;     /* number of vector, as postion in the linked list of vectors, starts with 0 */
     char *vecname;  /* name of the actual vector */
-    bool is_real;   /* TRUE if the actual vector has real data */
+    BOOL is_real;   /* TRUE if the actual vector has real data */
     void *pdvec;    /* a void pointer to struct dvec *d, the actual vector */
     void *pdvecscale; /* a void pointer to struct dvec *ds, the scale vector */
 } vecinfo, *pvecinfo;
@@ -216,11 +221,11 @@ typedef int (SendStat)(char*, int, void*);
    void* return pointer received from caller
 */
 /* asking for controlled exit */
-typedef int (ControlledExit)(int, bool, bool, int, void*);
+typedef int (ControlledExit)(int, BOOL, BOOL, int, void*);
 /*
    int   exit status
-   bool  if true: immediate unloading dll, if false: just set flag, unload is done when function has returned
-   bool  if true: exit upon 'quit', if false: exit due to ngspice.dll error
+   BOOL  if true: immediate unloading dll, if false: just set flag, unload is done when function has returned
+   BOOL  if true: exit upon 'quit', if false: exit due to ngspice.dll error
    int   identification number of calling ngspice shared lib
    void* return pointer received from caller
 */
@@ -242,9 +247,9 @@ typedef int (SendInitData)(pvecinfoall, int, void*);
 */
 
 /* indicate if background thread is running */
-typedef int (BGThreadRunning)(bool, int, void*);
+typedef int (BGThreadRunning)(BOOL, int, void*);
 /*
-   bool        true if background thread is running
+   BOOL        true if background thread is running
    int         identification number of calling ngspice shared lib
    void*       return pointer received from caller
 */
@@ -399,11 +404,11 @@ char** ngSpice_AllVecs(char* plotname);
 
 /* returns TRUE if ngspice is running in a second (background) thread */
 IMPEXP
-bool ngSpice_running(void);
+BOOL ngSpice_running(void);
 
 /* set a breakpoint in ngspice */
 IMPEXP
-bool ngSpice_SetBkpt(double time);
+BOOL ngSpice_SetBkpt(double time);
 
 
 #ifdef __cplusplus