diff --git a/src/flexdef.h b/src/flexdef.h
index 0852fd684..1127a4157 100644
--- a/src/flexdef.h
+++ b/src/flexdef.h
@@ -455,7 +455,7 @@ extern struct env_bundle_t env;
  * reject_really_used - same for REJECT
   */
 
-extern int syntaxerror, eofseen;
+extern bool syntaxerror, eofseen;
 extern int yymore_used, reject, real_reject, continued_action, in_rule;
 
 /* Variables used in the flex input routines:
@@ -568,7 +568,7 @@ extern int current_state_type;
 /* True if the input rules include a rule with both variable-length head
  * and trailing context, false otherwise.
  */
-extern int variable_trailing_context_rules;
+extern bool variable_trailing_context_rules;
 
 
 /* Variables for protos:
@@ -945,7 +945,7 @@ extern int copysingl(int, int);
 extern void dumpnfa(int);
 
 /* Finish up the processing for a rule. */
-extern void finish_rule(int, int, int, int, int);
+extern void finish_rule(int, bool, int, int, int);
 
 /* Connect two machines together. */
 extern int link_machines(int, int);
diff --git a/src/main.c b/src/main.c
index d2b688a71..c3f18f702 100644
--- a/src/main.c
+++ b/src/main.c
@@ -47,7 +47,7 @@ void readin(void);
 void set_up_initial_allocations(void);
 
 /* these globals are all defined and commented in flexdef.h */
-int     syntaxerror, eofseen;
+bool    syntaxerror, eofseen;
 int     yymore_used, reject, real_reject, continued_action, in_rule;
 int     datapos, dataline, linenum;
 FILE   *skelfile = NULL;
@@ -65,7 +65,7 @@ int    *firstst, *lastst, *finalst, *transchar, *trans1, *trans2;
 int    *accptnum, *assoc_rule, *state_type;
 int    *rule_type, *rule_linenum, *rule_useful;
 int     current_state_type;
-int     variable_trailing_context_rules;
+bool    variable_trailing_context_rules;
 int     numtemps, numprots, protprev[MSP], protnext[MSP], prottbl[MSP];
 int     protcomst[MSP], firstprot, lastprot, protsave[PROT_SAVE_SIZE];
 int     numecs, nextecm[CSIZE + 1], ecgroup[CSIZE + 1], nummecs,
@@ -1166,7 +1166,8 @@ void flexinit (int argc, char **argv)
 	numas = numsnpairs = tmpuses = 0;
 	numecs = numeps = eps2 = num_reallocs = hshcol = dfaeql = totnst =
 	    0;
-	numuniq = numdup = hshsave = eofseen = datapos = dataline = 0;
+	numuniq = numdup = hshsave = datapos = dataline = 0;
+	eofseen = false;
 	num_backing_up = onesp = numprots = 0;
 	variable_trailing_context_rules = bol_needed = false;
 
diff --git a/src/nfa.c b/src/nfa.c
index 47faecc6d..16e32a723 100644
--- a/src/nfa.c
+++ b/src/nfa.c
@@ -191,7 +191,7 @@ int     dupmachine (int mach)
  * context has variable length.
  */
 
-void    finish_rule (int mach, int variable_trail_rule, int headcnt, int trailcnt,
+void    finish_rule (int mach, bool variable_trail_rule, int headcnt, int trailcnt,
 		     int pcont_act)
 {
 	char    action_text[MAXLINE];
diff --git a/src/parse.y b/src/parse.y
index 1b0d64b4d..7d8a3ef3b 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -68,7 +68,9 @@
 #include "tables.h"
 
 int pat, scnum, eps, headcnt, trailcnt, lastchar, i, rulelen;
-int trlcontxt, xcluflg, currccl, cclsorted, varlength, variable_trail_rule;
+static int currccl;
+bool trlcontxt;
+static bool xcluflg, cclsorted, varlength, variable_trail_rule;
 
 int *scon_stk;
 int scon_stk_ptr;
diff --git a/src/scan.l b/src/scan.l
index 9fd3453e9..53e249873 100644
--- a/src/scan.l
+++ b/src/scan.l
@@ -40,7 +40,7 @@
 
 #include "parse.h"
 extern bool tablesverify, tablesext;
-extern int trlcontxt; /* Set in  parse.y for each rule. */
+extern bool trlcontxt; /* Set in parse.y for each rule. */
 extern const char *escaped_qstart, *escaped_qend;
 
 #define M4QSTART "[""["
@@ -155,10 +155,10 @@ void context_member(char *, const char *);
 %}
 %%
 	static int bracelevel, didadef, indented_code;
-	static int doing_rule_action = false;
-	static int option_sense;
+	static bool doing_rule_action = false;
+	static bool option_sense;
 
-	int doing_codeblock = false;
+	static bool doing_codeblock = false;
 	int brace_depth=0, brace_start_line=0;
 	char nmdef[MAXLINE];
 
@@ -395,7 +395,7 @@ void context_member(char *, const char *);
 	main		{
 			ctrl.do_main = option_sense;
 			/* Override yywrap */
-			if( option_sense == true )
+			if (option_sense)
                 		ctrl.do_yywrap = false;
 			}
 	meta-ecs	ctrl.usemecs = option_sense;
@@ -471,7 +471,7 @@ void context_member(char *, const char *);
 	tables-file         return TOK_TABLES_FILE;
 	tables-verify   {
                     tablesverify = option_sense;
-                    if(!tablesext && option_sense)
+                    if (!tablesext && option_sense)
                         tablesext = true;
                     }
 
diff --git a/src/yylex.c b/src/yylex.c
index 9a2e59f83..32fdfd858 100644
--- a/src/yylex.c
+++ b/src/yylex.c
@@ -51,7 +51,7 @@ int     yylex (void)
 		toktype = flexscan ();
         }
 	if (toktype == EOF || toktype == 0) {
-		eofseen = 1;
+		eofseen = true;
 
 		if (sectnum == 1) {
 			synerr (_("premature EOF"));