diff --git a/backend/medical.c b/backend/medical.c
index ce891b44..cb989677 100644
--- a/backend/medical.c
+++ b/backend/medical.c
@@ -48,20 +48,20 @@ int pharma_one(struct zint_symbol *symbol, unsigned char source[])
 	unsigned long int tester;
 	int counter;
 	char inter[17];
-	int errno;
+	int _errno_;
 	char dest[1000];
 	
-	errno = 0;
+	_errno_ = 0;
 	strcpy(dest, "");
 
 	if(strlen(source) > 6) {
 		strcpy(symbol->errtxt, "error: input too long");
 		return ERROR_TOO_LONG;
 	}
-	errno = is_sane(NESET, source);
-	if(errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(NESET, source);
+	if(_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: invalid characters in data");
-		return errno;
+		return _errno_;
 	}
 
 	strcpy(inter, "");
@@ -94,7 +94,7 @@ int pharma_one(struct zint_symbol *symbol, unsigned char source[])
 	
 	expand(symbol, dest);
 	strcpy(symbol->text, "");
-	return errno;
+	return _errno_;
 }
 
 int pharma_two_calc(struct zint_symbol *symbol, unsigned char source[], char dest[])
@@ -107,9 +107,9 @@ int pharma_two_calc(struct zint_symbol *symbol, unsigned char source[], char des
 	unsigned long int tester;
 	int counter;
 	char inter[17];
-	int errno;
+	int _errno_;
 	
-	errno = 0;
+	_errno_ = 0;
 	strcpy(dest, "");
 	
 	strcpy(inter, "");
@@ -145,7 +145,7 @@ int pharma_two_calc(struct zint_symbol *symbol, unsigned char source[], char des
 	}
 	dest[strlen(inter)] = '\0';
 	
-	return errno;
+	return _errno_;
 }
 
 int pharma_two(struct zint_symbol *symbol, unsigned char source[])
@@ -154,21 +154,21 @@ int pharma_two(struct zint_symbol *symbol, unsigned char source[])
 	char height_pattern[200];
 	unsigned int loopey;
 	int writer;
-	int errno = 0;
+	int _errno_ = 0;
 	strcpy(height_pattern, "");
 
 	if(strlen(source) > 8) {
 		strcpy(symbol->errtxt, "error: input too long");
 		return ERROR_TOO_LONG;
 	}
-	errno = is_sane(NESET, source);
-	if(errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(NESET, source);
+	if(_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: invalid characters in data");
-		return errno;
+		return _errno_;
 	}
-	errno = pharma_two_calc(symbol, source, height_pattern);
-	if(errno != 0) {
-		return errno;
+	_errno_ = pharma_two_calc(symbol, source, height_pattern);
+	if(_errno_ != 0) {
+		return _errno_;
 	}
 
 	writer = 0;
@@ -188,16 +188,16 @@ int pharma_two(struct zint_symbol *symbol, unsigned char source[])
 	symbol->width = writer - 1;
 	
 	strcpy(symbol->text, "");
-	return errno;
+	return _errno_;
 }
 
 int codabar(struct zint_symbol *symbol, unsigned char source[])
 { /* The Codabar system consisting of simple substitution */
 
-	int i, errno;
+	int i, _errno_;
 	char dest[1000];
 	
-	errno = 0;
+	_errno_ = 0;
 	strcpy(dest, "");
 
 	if(strlen(source) > 60) { /* No stack smashing please */
@@ -205,10 +205,10 @@ int codabar(struct zint_symbol *symbol, unsigned char source[])
 		return ERROR_TOO_LONG;
 	}
 	to_upper(source);
-	errno = is_sane(CASET, source);
-	if(errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(CASET, source);
+	if(_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: invalid characters in data");
-		return errno;
+		return _errno_;
 	}
 
 	/* Codabar must begin and end with the characters A, B, C or D */
@@ -233,5 +233,5 @@ int codabar(struct zint_symbol *symbol, unsigned char source[])
 	
 	expand(symbol, dest);
 	strcpy(symbol->text, source);
-	return errno;
+	return _errno_;
 }
diff --git a/backend/ps.c b/backend/ps.c
index cdeb6934..e7720dd5 100644
--- a/backend/ps.c
+++ b/backend/ps.c
@@ -37,7 +37,7 @@ int ps_plot(struct zint_symbol *symbol)
 	FILE *feps;
 	int fgred, fggrn, fgblu, bgred, bggrn, bgblu;
 	float red_ink, green_ink, blue_ink, red_paper, green_paper, blue_paper;
-	int errno = 0;
+	int _errno_ = 0;
 	int textoffset, xoffset, yoffset, textdone, main_width;
 	char textpart[10], addon[6];
 	int large_bar_count, comp_offset;
@@ -67,13 +67,13 @@ int ps_plot(struct zint_symbol *symbol)
 		strcpy(symbol->errtxt, "error: malformed background colour target");
 		return ERROR_INVALID_OPTION;
 	}
-	errno = is_sane(SSET, symbol->fgcolour);
-	if (errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(SSET, symbol->fgcolour);
+	if (_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: malformed foreground colour target");
 		return ERROR_INVALID_OPTION;
 	}
-	errno = is_sane(SSET, symbol->bgcolour);
-	if (errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(SSET, symbol->bgcolour);
+	if (_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: malformed background colour target");
 		return ERROR_INVALID_OPTION;
 	}
@@ -785,6 +785,6 @@ int ps_plot(struct zint_symbol *symbol)
 	
 	fclose(feps);
 	
-	return errno;
+	return _errno_;
 }
 
diff --git a/backend/rss.c b/backend/rss.c
index e391e2cb..8595b93e 100644
--- a/backend/rss.c
+++ b/backend/rss.c
@@ -141,7 +141,7 @@ void getRSSwidths(int val, int n, int elements, int maxWidth, int noNarrow)
 
 int rss14(struct zint_symbol *symbol, unsigned char source[])
 { /* GS1 DataBar-14 */
-	int errno = 0, i, j, read, mask;
+	int _errno_ = 0, i, j, read, mask;
 	short int accum[112], left_reg[112], right_reg[112], x_reg[112], y_reg[112];
 	int data_character[4], data_group[4], v_odd[4], v_even[4];
 	int data_widths[8][4], checksum, c_left, c_right, total_widths[46], writer;
@@ -154,10 +154,10 @@ int rss14(struct zint_symbol *symbol, unsigned char source[])
 		strcpy(symbol->errtxt, "error: input too long");
 		return ERROR_TOO_LONG;
 	}
-	errno = is_sane(NESET, source);
-	if(errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(NESET, source);
+	if(_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: invalid characters in data");
-		return errno;
+		return _errno_;
 	}
 	
 	/* make some room for a separator row for composite symbols */
@@ -632,12 +632,12 @@ int rss14(struct zint_symbol *symbol, unsigned char source[])
 	}
 
 	
-	return errno;
+	return _errno_;
 }
 
 int rsslimited(struct zint_symbol *symbol, unsigned char source[])
 { /* GS1 DataBar Limited */
-	int errno = 0, i, mask;
+	int _errno_ = 0, i, mask;
 	short int accum[112], left_reg[112], right_reg[112], x_reg[112], y_reg[112];
 	int left_group, right_group, left_odd, left_even, right_odd, right_even;
 	int left_character, right_character, left_widths[14], right_widths[14];
@@ -651,10 +651,10 @@ int rsslimited(struct zint_symbol *symbol, unsigned char source[])
 		strcpy(symbol->errtxt, "error: input too long");
 		return ERROR_TOO_LONG;
 	}
-	errno = is_sane(NESET, source);
-	if(errno == ERROR_INVALID_DATA) {
+	_errno_ = is_sane(NESET, source);
+	if(_errno_ == ERROR_INVALID_DATA) {
 		strcpy(symbol->errtxt, "error: invalid characters in data");
-		return errno;
+		return _errno_;
 	}
 	
 	/* make some room for a separator row for composite symbols */
@@ -898,7 +898,7 @@ int rsslimited(struct zint_symbol *symbol, unsigned char source[])
 	
 	concat(symbol->text, hrt);
 	
-	return errno;
+	return _errno_;
 }
 
 int general_rules(char field[], char type[])