diff --git a/config.h.in b/config.h.in
index 681504ed1..fb64d227b 100644
--- a/config.h.in
+++ b/config.h.in
@@ -282,6 +282,9 @@
 /* Define to 1 if you have the `fexecve' function. */
 #undef HAVE_FEXECVE
 
+/* Define to 1 if you have the `fmemopen' function. */
+#undef HAVE_FMEMOPEN
+
 /* Define to 1 if you have the `fnmatch' function. */
 #undef HAVE_FNMATCH
 
diff --git a/configure b/configure
index 478a6bc6f..7820bfc67 100755
--- a/configure
+++ b/configure
@@ -3220,6 +3220,7 @@ as_fn_append ac_header_c_list " sys/sysmacros.h sys_sysmacros_h HAVE_SYS_SYSMACR
 as_fn_append ac_header_c_list " sys/syscall.h sys_syscall_h HAVE_SYS_SYSCALL_H"
 as_fn_append ac_header_c_list " sys/statvfs.h sys_statvfs_h HAVE_SYS_STATVFS_H"
 as_fn_append ac_func_c_list " fexecve HAVE_FEXECVE"
+as_fn_append ac_func_c_list " fmemopen HAVE_FMEMOPEN"
 as_fn_append ac_func_c_list " killpg HAVE_KILLPG"
 as_fn_append ac_func_c_list " nl_langinfo HAVE_NL_LANGINFO"
 as_fn_append ac_func_c_list " faccessat HAVE_FACCESSAT"
@@ -20167,6 +20168,7 @@ done
 
 
 
+
 case "$host_os" in
     hpux*)
 	if test X"$ac_cv_func_pread" = X"yes"; then
diff --git a/configure.ac b/configure.ac
index 2697c9e35..e589b26db 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2685,7 +2685,7 @@ dnl
 dnl Function checks
 dnl
 AC_FUNC_GETGROUPS
-AC_CHECK_FUNCS_ONCE([fexecve killpg nl_langinfo faccessat wordexp getauxval fseeko])
+AC_CHECK_FUNCS_ONCE([fexecve fmemopen killpg nl_langinfo faccessat wordexp getauxval fseeko])
 case "$host_os" in
     hpux*)
 	if test X"$ac_cv_func_pread" = X"yes"; then
diff --git a/lib/iolog/regress/fuzz/fuzz_iolog_json.c b/lib/iolog/regress/fuzz/fuzz_iolog_json.c
index 9ab3c0498..a7c397e0c 100644
--- a/lib/iolog/regress/fuzz/fuzz_iolog_json.c
+++ b/lib/iolog/regress/fuzz/fuzz_iolog_json.c
@@ -34,13 +34,39 @@
 
 #include "iolog_json.h"
 
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+static FILE *
+open_data(const uint8_t *data, size_t size)
+{
+#ifdef HAVE_FMEMOPEN
+    /* Operate in-memory. */
+    return fmemopen((void *)data, size, "r");
+#else
+    char tempfile[] = "/tmp/json.XXXXXX";
+    size_t nwritten;
+    int fd;
+
+    /* Use (unlinked) temporary file. */
+    fd = mkstemp(tempfile);
+    if (fd == -1)
+	return NULL;
+    unlink(tempfile);
+    nwritten = write(fd, data, size);
+    if (nwritten != size) {
+	close(fd);
+	return NULL;
+    }
+    lseek(fd, 0, SEEK_SET);
+    return fdopen(fd, "r");
+#endif
+}
+
+int
+LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     struct eventlog *evlog = NULL;
     FILE *fp;
 
-    /* Operate in-memory. */
-    fp = fmemopen((void *)data, size, "r");
+    fp = open_data(data, size);
     if (fp == NULL)
         return 0;
 
diff --git a/lib/iolog/regress/fuzz/fuzz_iolog_legacy.c b/lib/iolog/regress/fuzz/fuzz_iolog_legacy.c
index 17dda622e..c15f84375 100644
--- a/lib/iolog/regress/fuzz/fuzz_iolog_legacy.c
+++ b/lib/iolog/regress/fuzz/fuzz_iolog_legacy.c
@@ -32,13 +32,39 @@
 #include "sudo_iolog.h"
 #include "sudo_util.h"
 
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+static FILE *
+open_data(const uint8_t *data, size_t size)
+{
+#ifdef HAVE_FMEMOPEN
+    /* Operate in-memory. */
+    return fmemopen((void *)data, size, "r");
+#else
+    char tempfile[] = "/tmp/legacy.XXXXXX";
+    size_t nwritten;
+    int fd;
+
+    /* Use (unlinked) temporary file. */
+    fd = mkstemp(tempfile);
+    if (fd == -1)
+	return NULL;
+    unlink(tempfile);
+    nwritten = write(fd, data, size);
+    if (nwritten != size) {
+	close(fd);
+	return NULL;
+    }
+    lseek(fd, 0, SEEK_SET);
+    return fdopen(fd, "r");
+#endif
+}
+
+int
+LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     struct eventlog *evlog = NULL;
     FILE *fp;
 
-    /* Operate in-memory. */
-    fp = fmemopen((void *)data, size, "r");
+    fp = open_data(data, size);
     if (fp == NULL)
         return 0;
 
diff --git a/lib/iolog/regress/fuzz/fuzz_iolog_timing.c b/lib/iolog/regress/fuzz/fuzz_iolog_timing.c
index 640fa731e..e83726456 100644
--- a/lib/iolog/regress/fuzz/fuzz_iolog_timing.c
+++ b/lib/iolog/regress/fuzz/fuzz_iolog_timing.c
@@ -40,7 +40,8 @@
 #include "sudo_iolog.h"
 #include "sudo_util.h"
 
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+int
+LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     struct iolog_file iolog_file = { true };
     struct timing_closure closure;
diff --git a/plugins/sudoers/regress/fuzz/fuzz_sudoers.c b/plugins/sudoers/regress/fuzz/fuzz_sudoers.c
index cf7ee4e76..edea66462 100644
--- a/plugins/sudoers/regress/fuzz/fuzz_sudoers.c
+++ b/plugins/sudoers/regress/fuzz/fuzz_sudoers.c
@@ -43,7 +43,34 @@ open_sudoers(const char *file, bool doedit, bool *keepopen)
     return NULL;
 }
 
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+static FILE *
+open_data(const uint8_t *data, size_t size)
+{
+#ifdef HAVE_FMEMOPEN
+    /* Operate in-memory. */
+    return fmemopen((void *)data, size, "r");
+#else
+    char tempfile[] = "/tmp/sudoers.XXXXXX";
+    size_t nwritten;
+    int fd;
+
+    /* Use (unlinked) temporary file. */
+    fd = mkstemp(tempfile);
+    if (fd == -1)
+	return NULL;
+    unlink(tempfile);
+    nwritten = write(fd, data, size);
+    if (nwritten != size) {
+	close(fd);
+	return NULL;
+    }
+    lseek(fd, 0, SEEK_SET);
+    return fdopen(fd, "r");
+#endif
+}
+
+int
+LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     FILE *fp;
 
@@ -51,8 +78,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
     if (size < 5)
         return 0;
 
-    /* Operate in-memory. */
-    fp = fmemopen((void *)data, size, "r");
+    fp = open_data(data, size);
     if (fp == NULL)
         return 0;
 
diff --git a/plugins/sudoers/regress/fuzz/fuzz_sudoers_ldif.c b/plugins/sudoers/regress/fuzz/fuzz_sudoers_ldif.c
index df98d9982..e1814b1ef 100644
--- a/plugins/sudoers/regress/fuzz/fuzz_sudoers_ldif.c
+++ b/plugins/sudoers/regress/fuzz/fuzz_sudoers_ldif.c
@@ -38,6 +38,32 @@ open_sudoers(const char *file, bool doedit, bool *keepopen)
     return fopen(file, "r");
 }
 
+static FILE *
+open_data(const uint8_t *data, size_t size)
+{
+#ifdef HAVE_FMEMOPEN
+    /* Operate in-memory. */
+    return fmemopen((void *)data, size, "r");
+#else
+    char tempfile[] = "/tmp/ldif.XXXXXX";
+    size_t nwritten;
+    int fd;
+
+    /* Use (unlinked) temporary file. */
+    fd = mkstemp(tempfile);
+    if (fd == -1)
+	return NULL;
+    unlink(tempfile);
+    nwritten = write(fd, data, size);
+    if (nwritten != size) {
+	close(fd);
+	return NULL;
+    }
+    lseek(fd, 0, SEEK_SET);
+    return fdopen(fd, "r");
+#endif
+}
+
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     struct sudoers_parse_tree parse_tree;
@@ -47,8 +73,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
     if (size < 5)
         return 0;
 
-    /* Operate in-memory. */
-    fp = fmemopen((void *)data, size, "r");
+    fp = open_data(data, size);
     if (fp == NULL)
         return 0;