diff --git a/src/interfaces/ecpg/test/pg_regress_ecpg.c b/src/interfaces/ecpg/test/pg_regress_ecpg.c
index 46b9e78fe59..a2d7b70d9a3 100644
--- a/src/interfaces/ecpg/test/pg_regress_ecpg.c
+++ b/src/interfaces/ecpg/test/pg_regress_ecpg.c
@@ -19,8 +19,9 @@
 #include "postgres_fe.h"
 
 #include "pg_regress.h"
+#include "common/string.h"
+#include "lib/stringinfo.h"
 
-#define LINEBUFSIZE 300
 
 static void
 ecpg_filter(const char *sourcefile, const char *outfile)
@@ -31,7 +32,7 @@ ecpg_filter(const char *sourcefile, const char *outfile)
 	 */
 	FILE	   *s,
 			   *t;
-	char		linebuf[LINEBUFSIZE];
+	StringInfoData linebuf;
 
 	s = fopen(sourcefile, "r");
 	if (!s)
@@ -46,13 +47,14 @@ ecpg_filter(const char *sourcefile, const char *outfile)
 		exit(2);
 	}
 
-	while (fgets(linebuf, LINEBUFSIZE, s))
+	initStringInfo(&linebuf);
+
+	while (pg_get_line_append(s, &linebuf))
 	{
 		/* check for "#line " in the beginning */
-		if (strstr(linebuf, "#line ") == linebuf)
+		if (strstr(linebuf.data, "#line ") == linebuf.data)
 		{
-			char	   *p = strchr(linebuf, '"');
-			char	   *n;
+			char	   *p = strchr(linebuf.data, '"');
 			int			plen = 1;
 
 			while (*p && (*(p + plen) == '.' || strchr(p + plen, '/') != NULL))
@@ -62,13 +64,15 @@ ecpg_filter(const char *sourcefile, const char *outfile)
 			/* plen is one more than the number of . and / characters */
 			if (plen > 1)
 			{
-				n = (char *) malloc(plen);
-				strlcpy(n, p + 1, plen);
-				replace_string(linebuf, n, "");
+				memmove(p + 1, p + plen, strlen(p + plen) + 1);
+				/* we don't bother to fix up linebuf.len */
 			}
 		}
-		fputs(linebuf, t);
+		fputs(linebuf.data, t);
+		resetStringInfo(&linebuf);
 	}
+
+	pfree(linebuf.data);
 	fclose(s);
 	fclose(t);
 }
@@ -87,40 +91,42 @@ ecpg_start_test(const char *testname,
 	PID_TYPE	pid;
 	char		inprg[MAXPGPATH];
 	char		insource[MAXPGPATH];
-	char	   *outfile_stdout,
+	StringInfoData testname_dash;
+	char		outfile_stdout[MAXPGPATH],
 				expectfile_stdout[MAXPGPATH];
-	char	   *outfile_stderr,
+	char		outfile_stderr[MAXPGPATH],
 				expectfile_stderr[MAXPGPATH];
-	char	   *outfile_source,
+	char		outfile_source[MAXPGPATH],
 				expectfile_source[MAXPGPATH];
 	char		cmd[MAXPGPATH * 3];
-	char	   *testname_dash;
 	char	   *appnameenv;
 
 	snprintf(inprg, sizeof(inprg), "%s/%s", inputdir, testname);
+	snprintf(insource, sizeof(insource), "%s.c", testname);
+
+	initStringInfo(&testname_dash);
+	appendStringInfoString(&testname_dash, testname);
+	replace_string(&testname_dash, "/", "-");
 
-	testname_dash = strdup(testname);
-	replace_string(testname_dash, "/", "-");
 	snprintf(expectfile_stdout, sizeof(expectfile_stdout),
 			 "%s/expected/%s.stdout",
-			 outputdir, testname_dash);
+			 outputdir, testname_dash.data);
 	snprintf(expectfile_stderr, sizeof(expectfile_stderr),
 			 "%s/expected/%s.stderr",
-			 outputdir, testname_dash);
+			 outputdir, testname_dash.data);
 	snprintf(expectfile_source, sizeof(expectfile_source),
 			 "%s/expected/%s.c",
-			 outputdir, testname_dash);
+			 outputdir, testname_dash.data);
 
-	/*
-	 * We can use replace_string() here because the replacement string does
-	 * not occupy more space than the replaced one.
-	 */
-	outfile_stdout = strdup(expectfile_stdout);
-	replace_string(outfile_stdout, "/expected/", "/results/");
-	outfile_stderr = strdup(expectfile_stderr);
-	replace_string(outfile_stderr, "/expected/", "/results/");
-	outfile_source = strdup(expectfile_source);
-	replace_string(outfile_source, "/expected/", "/results/");
+	snprintf(outfile_stdout, sizeof(outfile_stdout),
+			 "%s/results/%s.stdout",
+			 outputdir, testname_dash.data);
+	snprintf(outfile_stderr, sizeof(outfile_stderr),
+			 "%s/results/%s.stderr",
+			 outputdir, testname_dash.data);
+	snprintf(outfile_source, sizeof(outfile_source),
+			 "%s/results/%s.c",
+			 outputdir, testname_dash.data);
 
 	add_stringlist_item(resultfiles, outfile_stdout);
 	add_stringlist_item(expectfiles, expectfile_stdout);
@@ -134,18 +140,15 @@ ecpg_start_test(const char *testname,
 	add_stringlist_item(expectfiles, expectfile_source);
 	add_stringlist_item(tags, "source");
 
-	snprintf(insource, sizeof(insource), "%s.c", testname);
 	ecpg_filter(insource, outfile_source);
 
-	snprintf(inprg, sizeof(inprg), "%s/%s", inputdir, testname);
-
 	snprintf(cmd, sizeof(cmd),
 			 "\"%s\" >\"%s\" 2>\"%s\"",
 			 inprg,
 			 outfile_stdout,
 			 outfile_stderr);
 
-	appnameenv = psprintf("PGAPPNAME=ecpg/%s", testname_dash);
+	appnameenv = psprintf("PGAPPNAME=ecpg/%s", testname_dash.data);
 	putenv(appnameenv);
 
 	pid = spawn_process(cmd);
@@ -160,10 +163,7 @@ ecpg_start_test(const char *testname,
 	unsetenv("PGAPPNAME");
 	free(appnameenv);
 
-	free(testname_dash);
-	free(outfile_stdout);
-	free(outfile_stderr);
-	free(outfile_source);
+	free(testname_dash.data);
 
 	return pid;
 }
diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index d82e0189dcf..74fd026856e 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -31,8 +31,10 @@
 
 #include "common/logging.h"
 #include "common/restricted_token.h"
+#include "common/string.h"
 #include "common/username.h"
 #include "getopt_long.h"
+#include "lib/stringinfo.h"
 #include "libpq/pqcomm.h"		/* needed for UNIXSOCK_PATH() */
 #include "pg_config_paths.h"
 #include "pg_regress.h"
@@ -435,22 +437,32 @@ string_matches_pattern(const char *str, const char *pattern)
 }
 
 /*
- * Replace all occurrences of a string in a string with a different string.
- * NOTE: Assumes there is enough room in the target buffer!
+ * Replace all occurrences of "replace" in "string" with "replacement".
+ * The StringInfo will be suitably enlarged if necessary.
+ *
+ * Note: this is optimized on the assumption that most calls will find
+ * no more than one occurrence of "replace", and quite likely none.
  */
 void
-replace_string(char *string, const char *replace, const char *replacement)
+replace_string(StringInfo string, const char *replace, const char *replacement)
 {
+	int			pos = 0;
 	char	   *ptr;
 
-	while ((ptr = strstr(string, replace)) != NULL)
+	while ((ptr = strstr(string->data + pos, replace)) != NULL)
 	{
-		char	   *dup = pg_strdup(string);
+		/* Must copy the remainder of the string out of the StringInfo */
+		char	   *suffix = pg_strdup(ptr + strlen(replace));
 
-		strlcpy(string, dup, ptr - string + 1);
-		strcat(string, replacement);
-		strcat(string, dup + (ptr - string) + strlen(replace));
-		free(dup);
+		/* Truncate StringInfo at start of found string ... */
+		string->len = ptr - string->data;
+		/* ... and append the replacement (this restores the trailing '\0') */
+		appendStringInfoString(string, replacement);
+		/* Next search should start after the replacement */
+		pos = string->len;
+		/* Put back the remainder of the string */
+		appendStringInfoString(string, suffix);
+		free(suffix);
 	}
 }
 
@@ -521,7 +533,7 @@ convert_sourcefiles_in(const char *source_subdir, const char *dest_dir, const ch
 		char		prefix[MAXPGPATH];
 		FILE	   *infile,
 				   *outfile;
-		char		line[1024];
+		StringInfoData line;
 
 		/* reject filenames not finishing in ".source" */
 		if (strlen(*name) < 8)
@@ -551,15 +563,21 @@ convert_sourcefiles_in(const char *source_subdir, const char *dest_dir, const ch
 					progname, destfile, strerror(errno));
 			exit(2);
 		}
-		while (fgets(line, sizeof(line), infile))
+
+		initStringInfo(&line);
+
+		while (pg_get_line_append(infile, &line))
 		{
-			replace_string(line, "@abs_srcdir@", inputdir);
-			replace_string(line, "@abs_builddir@", outputdir);
-			replace_string(line, "@testtablespace@", testtablespace);
-			replace_string(line, "@libdir@", dlpath);
-			replace_string(line, "@DLSUFFIX@", DLSUFFIX);
-			fputs(line, outfile);
+			replace_string(&line, "@abs_srcdir@", inputdir);
+			replace_string(&line, "@abs_builddir@", outputdir);
+			replace_string(&line, "@testtablespace@", testtablespace);
+			replace_string(&line, "@libdir@", dlpath);
+			replace_string(&line, "@DLSUFFIX@", DLSUFFIX);
+			fputs(line.data, outfile);
+			resetStringInfo(&line);
 		}
+
+		pfree(line.data);
 		fclose(infile);
 		fclose(outfile);
 	}
diff --git a/src/test/regress/pg_regress.h b/src/test/regress/pg_regress.h
index ee6e0d42f40..726f9c90489 100644
--- a/src/test/regress/pg_regress.h
+++ b/src/test/regress/pg_regress.h
@@ -18,6 +18,8 @@
 #define INVALID_PID INVALID_HANDLE_VALUE
 #endif
 
+struct StringInfoData;			/* avoid including stringinfo.h here */
+
 /* simple list of strings */
 typedef struct _stringlist
 {
@@ -49,5 +51,6 @@ int			regression_main(int argc, char *argv[],
 							init_function ifunc, test_function tfunc);
 void		add_stringlist_item(_stringlist **listhead, const char *str);
 PID_TYPE	spawn_process(const char *cmdline);
-void		replace_string(char *string, const char *replace, const char *replacement);
+void		replace_string(struct StringInfoData *string,
+						   const char *replace, const char *replacement);
 bool		file_exists(const char *file);