diff -ur /tmp/e/base/src/as/asLibRoutines.c ./as/asLibRoutines.c
--- /tmp/e/base/src/as/asLibRoutines.c	2010-03-31 10:13:33.000000000 -0700
+++ ./as/asLibRoutines.c	2010-03-31 10:08:13.000000000 -0700
@@ -201,7 +201,7 @@
 	    fgetsRtn = fgets(mac_input_buffer,BUF_SIZE,stream);
 	    if(fgetsRtn) {
 		n = macExpandString(macHandle,mac_input_buffer,
-		    my_buffer,BUF_SIZE-1);
+		    my_buffer,BUF_SIZE);
 		if(n<0) {
 		    epicsPrintf("access security: macExpandString failed\n"
 			"input line: %s\n",mac_input_buffer);
diff -ur /tmp/e/base/src/dbStatic/dbLexRoutines.c ./dbStatic/dbLexRoutines.c
--- /tmp/e/base/src/dbStatic/dbLexRoutines.c	2010-03-31 10:13:43.000000000 -0700
+++ ./dbStatic/dbLexRoutines.c	2010-03-31 10:07:32.000000000 -0700
@@ -312,7 +312,7 @@
 			pinputFileNow->fp);
 		if(fgetsRtn) {
 		    n = macExpandString(macHandle,mac_input_buffer,
-			my_buffer,MY_BUFFER_SIZE-1);
+			my_buffer,MY_BUFFER_SIZE);
 		    if(n<0) {
 			errPrintf(0,__FILE__, __LINE__,
 			"macExpandString failed for file %s",
diff -ur /tmp/e/base/src/libCom/macLib/macCore.c ./libCom/macLib/macCore.c
--- /tmp/e/base/src/libCom/macLib/macCore.c	2010-03-31 10:13:49.000000000 -0700
+++ ./libCom/macLib/macCore.c	2010-03-31 10:11:42.000000000 -0700
@@ -69,11 +69,11 @@
 static long       expand( MAC_HANDLE *handle );
 static void       trans ( MAC_HANDLE *handle, MAC_ENTRY *entry, int level,
                           const char *term, const char **rawval, char **value,
-                          char *valend );
+                          char *lastValid );
 static void       refer ( MAC_HANDLE *handle, MAC_ENTRY *entry, int level,
-                          const char **rawval, char **value, char *valend );
+                          const char **rawval, char **value, char *lastValid );
 
-static void cpy2val( const char *src, char **value, char *valend );
+static void cpy2val( const char *src, char **value, char *lastValid );
 static char *Strdup( const char *string );
 
 
@@ -180,8 +180,7 @@
 
     char        *dest,          /* destination string */
 
-    long        maxlen )        /* maximum number of characters to copy */
-                                /* to destination string */
+    long        capacity )      /* capacity of destination buffer (dest) */
 {
     MAC_ENTRY entry;
     const char *s;
@@ -196,7 +195,11 @@
 
     /* debug output */
     if ( handle->debug & 1 )
-        printf( "macExpandString( %s, maxlen = %ld )\n", src, maxlen );
+        printf( "macExpandString( %s, capacity = %ld )\n", src, capacity );
+
+    /* Check size */
+    if (capacity <= 1)
+        return -1;
 
     /* expand raw values if necessary */
     if ( expand( handle ) < 0 )
@@ -211,7 +214,7 @@
     s  = src;
     d  = dest;
     *d = '\0';
-    trans( handle, &entry, 0, "", &s, &d, d + maxlen );
+    trans( handle, &entry, 0, "", &s, &d, d + capacity - 1 );
 
     /* return +/- #chars copied depending on successful expansion */
     length = d - dest;
@@ -295,8 +298,7 @@
     char        *value,         /* string to receive macro value or name */
                                 /* argument if macro is undefined */
 
-    long        maxlen )        /* maximum number of characters to copy */
-                                /* to value */
+    long        capacity )      /* capcity of destination buffer (value) */
 {
     MAC_ENTRY   *entry;         /* pointer to this macro's entry structure */
     long        length;         /* number of characters returned */
@@ -314,31 +316,31 @@
     /* look up macro name */
     entry = lookup( handle, name, FALSE );
 
-    /* if maxlen <= 0 or VALUE == NULL just return -1 / 0 for undefined /
+    /* if capacity <= 1 or VALUE == NULL just return -1 / 0 for undefined /
        defined macro */
-    if ( maxlen <= 0 || value == NULL ) {
+    if ( capacity <= 1 || value == NULL ) {
         return ( entry == NULL ) ? -1 : 0;
     }
 
     /* if not found, copy name to value and return minus #chars copied */
     if ( entry == NULL ) {
-        strncpy( value, name, maxlen );
-        return ( value[maxlen-1] == '\0' ) ? - (long) strlen( name ) : -maxlen;
+        strncpy( value, name, capacity );
+        return ( value[capacity-1] == '\0' ) ? - (long) strlen( name ) : -capacity;
     }
 
     /* expand raw values if necessary; if fail (can only fail because of
        memory allocation failure), return same as if not found */
     if ( expand( handle ) < 0 ) {
         errlogPrintf( "macGetValue: failed to expand raw values\n" );
-        strncpy( value, name, maxlen );
-        return ( value[maxlen-1] == '\0' ) ? - (long) strlen( name ) : -maxlen;
+        strncpy( value, name, capacity );
+        return ( value[capacity-1] == '\0' ) ? - (long) strlen( name ) : -capacity;
     }
 
     /* copy value and return +/- #chars copied depending on successful
        expansion */
 /* FIXME: nul-terminator */
-    strncpy( value, entry->value, maxlen );
-    length = ( value[maxlen-1] == '\0' ) ? entry->length : maxlen;
+    strncpy( value, entry->value, capacity );
+    length = ( value[capacity-1] == '\0' ) ? entry->length : capacity;
 
     return ( entry->error ) ? -length : length;
 }
@@ -677,7 +679,7 @@
  */
 static void trans( MAC_HANDLE *handle, MAC_ENTRY *entry, int level,
                    const char *term, const char **rawval, char **value,
-                   char *valend )
+                   char *lastValid )
 {
     char quote;
     const char *r;
@@ -694,8 +696,8 @@
 
     /* debug output */
     if ( handle->debug & 2 )
-        printf( "trans-> entry = %p, level = %d, maxlen = %u, discard = %s, "
-        "rawval = %s\n", entry, level, (unsigned int)(valend - *value), discard ? "T" : "F", *rawval );
+        printf( "trans-> entry = %p, level = %d, capacity = %u, discard = %s, "
+        "rawval = %s\n", entry, level, (unsigned int)(lastValid - *value), discard ? "T" : "F", *rawval );
 
     /* initially not in quotes */
     quote = 0;
@@ -723,23 +725,23 @@
         /* macros are not expanded in single quotes */
         if ( macRef && quote != '\'' ) {
             /* Handle macro reference */
-            refer ( handle, entry, level, &r, &v, valend );
+            refer ( handle, entry, level, &r, &v, lastValid );
         }
 
         else {
             /* handle escaped characters (escape is discarded if in name) */
             if ( *r == '\\' && *( r + 1 ) != '\0' ) {
-                if ( v < valend && !discard ) *v++ = '\\';
-                if ( v < valend ) *v++ = *++r;
+                if ( v < lastValid && !discard ) *v++ = '\\';
+                if ( v < lastValid ) *v++ = *++r;
             }
 
             /* copy character to output */
             else {
-                if ( v < valend ) *v++ = *r;
+                if ( v < lastValid ) *v++ = *r;
             }
 
             /* ensure string remains properly terminated */
-            if ( v <= valend ) *v   = '\0';
+            if ( v <= lastValid ) *v   = '\0';
         }
     }
 
@@ -763,7 +765,7 @@
  * pulled out for ease of understanding.
  */
 static void refer ( MAC_HANDLE *handle, MAC_ENTRY *entry, int level,
-                    const char **rawval, char **value, char *valend )
+                    const char **rawval, char **value, char *lastValid )
 {
     const char *r = *rawval;
     char *v = *value;
@@ -777,8 +779,8 @@
 
     /* debug output */
     if ( handle->debug & 2 )
-        printf( "refer-> entry = %p, level = %d, maxlen = %u, rawval = %s\n",
-                entry, level, (unsigned int)(valend - *value), *rawval );
+        printf( "refer-> entry = %p, level = %d, capacity = %u, rawval = %s\n",
+                entry, level, (unsigned int)(lastValid - *value), *rawval );
 
     /* step over '$(' or '${' */
     r++;
@@ -858,13 +860,13 @@
             /* reference is good, use it */
             if ( !handle->dirty ) {
                 /* copy the already-expanded value, and its error status! */
-                cpy2val( refentry->value, &v, valend );
+                cpy2val( refentry->value, &v, lastValid );
                 entry->error = refentry->error;
             } else {
                 /* translate raw value */
                 const char *rv = refentry->rawval;
                 refentry->visited = TRUE;
-                trans( handle, entry, level + 1, "", &rv, &v, valend );
+                trans( handle, entry, level + 1, "", &rv, &v, lastValid );
                 refentry->visited = FALSE;
             }
             goto cleanup;
@@ -881,7 +883,7 @@
         /* no macro found by this name */
         if ( defval ) {
             /* there was a default value, translate that instead */
-            trans( handle, entry, level + 1, macEnd+1, &defval, &v, valend );
+            trans( handle, entry, level + 1, macEnd+1, &defval, &v, lastValid );
             goto cleanup;
         }
         entry->error = TRUE;
@@ -893,10 +895,10 @@
     }
 
     /* Bad reference, insert $(name,errval) */
-    if ( v < valend ) *v++ = '$';
-    if ( v < valend ) *v++ = '(';
-    cpy2val( refname, &v, valend );
-    cpy2val( errval, &v, valend );
+    if ( v < lastValid ) *v++ = '$';
+    if ( v < lastValid ) *v++ = '(';
+    cpy2val( refname, &v, lastValid );
+    cpy2val( errval, &v, lastValid );
 
 cleanup:
     if (pop) {
@@ -917,10 +919,10 @@
  * Copy a string, honoring the 'end of destination string' pointer
  * Returns with **value pointing to the '\0' terminator
  */
-static void cpy2val(const char *src, char **value, char *valend)
+static void cpy2val(const char *src, char **value, char *lastValid)
 {
     char *v = *value;
-    while ((v < valend) && (*v = *src++)) { v++; }
+    while ((v < lastValid) && (*v = *src++)) { v++; }
     *v = '\0';
     *value = v;
 }
diff -ur /tmp/e/base/src/libCom/macLib/macLib.h ./libCom/macLib/macLib.h
--- /tmp/e/base/src/libCom/macLib/macLib.h	2010-03-31 10:13:49.000000000 -0700
+++ ./libCom/macLib/macLib.h	2010-03-31 10:24:33.000000000 -0700
@@ -65,7 +65,7 @@
     int         falseTrue       /*0 means issue, 1 means suppress*/
 );
 
-epicsShareFunc long             /* #chars copied, <0 if any macros are */
+epicsShareFunc long             /* #chars copied (not including trailing nul), <0 if any macros are */
                                 /* undefined */
 epicsShareAPI macExpandString(
     MAC_HANDLE  *handle,        /* opaque handle */
@@ -74,8 +74,7 @@
 
     char        *dest,          /* destination string */
 
-    long        maxlen          /* maximum number of characters to copy */
-                                /* to destination string */
+    long        capacity        /* capacity of destination buffer (dest) */
 );
 
 
@@ -97,8 +96,7 @@
     char        *value,         /* string to receive macro value or name */
                                 /* argument if macro is undefined */
 
-    long        maxlen          /* maximum number of characters to copy */
-                                /* to value */
+    long        capacity        /* capacity of destination buffer (value) */
 );
 
 epicsShareFunc long             /* 0 = OK; <0 = ERROR */