diff --git a/src/mod_fastcgi.c b/src/mod_fastcgi.c
--- a/src/mod_fastcgi.c
+++ b/src/mod_fastcgi.c
@@ -693,6 +693,7 @@
 
 static int env_add(char_array *env, const char *key, size_t key_len, const char *val, size_t val_len) {
 	char *dst;
+	size_t i;
 
 	if (!key || !val) return -1;
 
@@ -701,6 +702,14 @@
 	dst[key_len] = '=';
 	/* add the \0 from the value */
 	memcpy(dst + key_len + 1, val, val_len + 1);
+
+	for (i = 0; i < env->used; i++)
+		if (strlen(env->ptr[i]) >= key_len + 1 &&
+		    memcmp(dst, env->ptr[i], key_len + 1) == 0) {
+			free(env->ptr[i]);
+			env->ptr[i] = dst;
+			return 0;
+		}
 
 	if (env->size == 0) {
 		env->size = 16;
diff --git a/src/mod_scgi.c b/src/mod_scgi.c
--- a/src/mod_scgi.c
+++ b/src/mod_scgi.c
@@ -583,6 +583,7 @@
 
 static int env_add(char_array *env, const char *key, size_t key_len, const char *val, size_t val_len) {
 	char *dst;
+	size_t i;
 
 	if (!key || !val) return -1;
 
@@ -591,6 +592,14 @@
 	dst[key_len] = '=';
 	/* add the \0 from the value */
 	memcpy(dst + key_len + 1, val, val_len + 1);
+
+	for (i = 0; i < env->used; i++)
+		if (strlen(env->ptr[i]) >= key_len + 1 &&
+		    memcmp(dst, env->ptr[i], key_len + 1) == 0) {
+			free(env->ptr[i]);
+			env->ptr[i] = dst;
+			return 0;
+		}
 
 	if (env->size == 0) {
 		env->size = 16;