diff --git a/main/Makefile b/main/Makefile
index 9630b635c8..9d75208da7 100644
--- a/main/Makefile
+++ b/main/Makefile
@@ -101,21 +101,21 @@ editline/libedit.a: CHECK_SUBDIR
 db1-ast/libdb1.a: CHECK_SUBDIR
 	_ASTCFLAGS="$(_ASTCFLAGS)" ASTCFLAGS="$(ASTCFLAGS) -Wno-strict-aliasing" $(MAKE) -C db1-ast libdb1.a
 
-ifneq ($(BISON),)
+ifneq ($(BISON),:)
 ast_expr2.c ast_expr2.h: ast_expr2.y
 else
 ast_expr2.c ast_expr2.h:
 endif
 	$(ECHO_PREFIX) echo "   [BISON] $< -> $@"
-	$(CMD_PREFIX) bison -o $@ -d --name-prefix=ast_yy ast_expr2.y
+	$(CMD_PREFIX) $(BISON) -o $@ -d --name-prefix=ast_yy ast_expr2.y
 
-ifneq ($(FLEX),)
+ifneq ($(FLEX),:)
 ast_expr2f.c: ast_expr2.fl
 else
 ast_expr2f.c:
 endif
 	$(ECHO_PREFIX) echo "   [FLEX] $< -> $@"
-	$(CMD_PREFIX) flex -o $@ ast_expr2.fl
+	$(CMD_PREFIX) $(FLEX) -o $@ ast_expr2.fl
 	$(CMD_PREFIX) sed 's@#if __STDC_VERSION__ >= 199901L@#if !defined __STDC_VERSION__ || __STDC_VERSION__ >= 199901L@' $@ > $@.fix
 	$(CMD_PREFIX) echo "#include \"asterisk.h\"" > $@
 	$(CMD_PREFIX) echo >> $@
diff --git a/res/Makefile b/res/Makefile
index 1badb79e15..b842dec789 100644
--- a/res/Makefile
+++ b/res/Makefile
@@ -45,22 +45,22 @@ $(if $(filter res_snmp,$(EMBEDDED_MODS)),modules.link,res_snmp.so): snmp/agent.o
 
 $(if $(filter res_ael_share,$(EMBEDDED_MODS)),modules.link,res_ael_share.so): ael/ael_lex.o ael/ael.tab.o ael/pval.o
 
-ifneq ($(FLEX),)
+ifneq ($(FLEX),:)
 ael/ael_lex.c: ael/ael.flex
 else
 ael/ael_lex.c:
 endif
 	$(ECHO_PREFIX) echo "   [FLEX] $< -> $@"
-	$(CMD_PREFIX) (cd ael; flex ael.flex; sed -e "/begin standard C headers/i#include \"asterisk.h\"" ael_lex.c > zz; mv zz ael_lex.c)
+	$(CMD_PREFIX) (cd ael; $(FLEX) ael.flex; sed -e "/begin standard C headers/i#include \"asterisk.h\"" ael_lex.c > zz; mv zz ael_lex.c)
 	$(CMD_PREFIX) (cd ael; sed 's@#if __STDC_VERSION__ >= 199901L@#if !defined __STDC_VERSION__ || __STDC_VERSION__ >= 199901L@' ael_lex.c > zz; mv zz ael_lex.c)
 
-ifneq ($(BISON),)
+ifneq ($(BISON),:)
 ael/ael.tab.c ael/ael.tab.h: ael/ael.y
 else
 ael/ael.tab.c ael/ael.tab.h:
 endif
 	$(ECHO_PREFIX) echo "   [BISON] $< -> $@"
-	$(CMD_PREFIX) (cd ael; bison -v -d ael.y)
+	$(CMD_PREFIX) (cd ael; $(BISON) -v -d ael.y)
 
 ael/pval.o: ael/pval.c