diff --git a/compat/mingw.c b/compat/mingw.c
index fa5b9cd379..553e8f3ac4 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -736,10 +736,9 @@ void free_env(char **env)
 	free(env);
 }
 
-static int lookup_env(char **env, const char *name)
+static int lookup_env(char **env, const char *name, size_t nmln)
 {
 	int i;
-	size_t nmln = strlen(name);
 
 	for (i = 0; env[i]; i++) {
 		if (0 == strncmp(env[i], name, nmln)
@@ -750,15 +749,32 @@ static int lookup_env(char **env, const char *name)
 	return -1;
 }
 
-void env_unsetenv(char **env, const char *name)
+/*
+ * If name contains '=', then sets the variable, otherwise it unsets it
+ */
+char **env_setenv(char **env, const char *name)
 {
-	int i = lookup_env(env, name);
-	if (i < 0)
-		return;
+	char *eq = strchrnul(name, '=');
+	int i = lookup_env(env, name, eq-name);
 
-	free(env[i]);
-	for (; env[i]; i++)
-		env[i] = env[i+1];
+	if (i < 0) {
+		if (*eq) {
+			for (i = 0; env[i]; i++)
+				;
+			env = xrealloc(env, (i+2)*sizeof(*env));
+			env[i] = xstrdup(name);
+			env[i+1] = NULL;
+		}
+	}
+	else {
+		free(env[i]);
+		if (*eq)
+			env[i] = xstrdup(name);
+		else
+			for (; env[i]; i++)
+				env[i] = env[i+1];
+	}
+	return env;
 }
 
 /* this is the first function to call into WS_32; initialize it */
diff --git a/git-compat-util.h b/git-compat-util.h
index 12426951fa..120f88c943 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -638,7 +638,7 @@ sig_handler_t mingw_signal(int sig, sig_handler_t handler);
 
 char **copy_environ(void);
 void free_environ(void);
-void env_unsetenv(char **env, const char *name);
+char **env_setenv(char **env, const char *name);
 
 #endif /* __MINGW32__ */
 
diff --git a/run-command.c b/run-command.c
index 8e0daab62a..37d4d7fafc 100644
--- a/run-command.c
+++ b/run-command.c
@@ -146,12 +146,8 @@ int start_command(struct child_process *cmd)
 		die("chdir in start_command() not implemented");
 	if (cmd->env) {
 		env = copy_environ();
-		for (; *cmd->env; cmd->env++) {
-			if (strchr(*cmd->env, '='))
-				die("setting environment in start_command() not implemented");
-			else
-				env_unsetenv(env, *cmd->env);
-		}
+		for (; *cmd->env; cmd->env++)
+			env = env_setenv(env, *cmd->env);
 	}
 
 	if (cmd->git_cmd) {