diff --git a/configure.ac b/configure.ac
index 185ada350e1..4204b86fa15 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,7 +1,7 @@
 dnl
 dnl autoconf for Pacemaker
 dnl
-dnl Copyright 2009-2025 the Pacemaker project contributors
+dnl Copyright 2009-2026 the Pacemaker project contributors
 dnl
 dnl The version control history for this file may have further details.
 dnl
@@ -1234,6 +1234,42 @@ AS_IF([test x"$have_sscanf_m" = x"yes"],
       [AC_DEFINE([HAVE_SSCANF_M], [1],
                  [Define to 1 if sscanf %m modifier is available])])
 
+AC_RUN_IFELSE([AC_LANG_PROGRAM([[#include <time.h>]], [[
+    char s[200];
+    time_t t;
+    struct tm *tmp;
+    size_t rc;
+
+    t = time(NULL);
+    tmp = localtime(&t);
+    rc = strftime(s, sizeof(s), "%3S", tmp);
+    return rc != 3;
+                               ]])],
+              [have_strftime_width="yes"],
+              [have_strftime_width="no"],
+              [have_strftime_width="no"])
+AS_IF([test x"$have_strftime_width" = x"yes"],
+      [AC_DEFINE([HAVE_STRFTIME_WIDTH], [1],
+                 [Define to 1 if strftime supports field width])])
+
+AC_RUN_IFELSE([AC_LANG_PROGRAM([[#include <time.h>]], [[
+    char s[200];
+    time_t t;
+    struct tm *tmp;
+    size_t rc;
+
+    t = time(NULL);
+    tmp = localtime(&t);
+    rc = strftime(s, sizeof(s), "% abcd", tmp);
+    return rc != 0;
+                               ]])],
+              [have_strftime_empty_spec_fails="yes"],
+              [have_strftime_empty_spec_fails="no"],
+              [have_strftime_empty_spec_fails="no"])
+AS_IF([test x"$have_strftime_empty_spec_fails" = x"yes"],
+      [AC_DEFINE([HAVE_STRFTIME_EMPTY_SPEC_FAILS], [1],
+                 [Define to 1 if a percent with no specifier fails])])
+
 dnl ========================================================================
 dnl   bzip2
 dnl ========================================================================
diff --git a/lib/common/tests/iso8601/pcmk__time_format_hr_test.c b/lib/common/tests/iso8601/pcmk__time_format_hr_test.c
index ead23e9c8fc..3e52aea7b8a 100644
--- a/lib/common/tests/iso8601/pcmk__time_format_hr_test.c
+++ b/lib/common/tests/iso8601/pcmk__time_format_hr_test.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2024-2025 the Pacemaker project contributors
+ * Copyright 2024-2026 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
@@ -85,24 +85,43 @@ no_specifiers(void **state)
      * as "%%".
      */
     assert_hr_format("this has a literal % in it",
+#ifdef HAVE_STRFTIME_EMPTY_SPEC_FAILS
+                     NULL, NULL, 0);
+#else
                      "this has a literal % in it",
                      // *BSD strftime() strips single %
                      "this has a literal  in it", 0);
+#endif
+
     assert_hr_format("this has a literal %01 in it",
+#ifdef HAVE_STRFTIME_EMPTY_SPEC_FAILS
+                     NULL, NULL, 0);
+#else
                      "this has a literal %01 in it",
                      // *BSD strftime() strips %0
                      "this has a literal 1 in it", 0);
+#endif
+
     assert_hr_format("%2 this starts and ends with %",
+#ifdef HAVE_STRFTIME_EMPTY_SPEC_FAILS
+                     NULL, NULL, 0);
+#else
                      "%2 this starts and ends with %",
                      // *BSD strftime() strips % in front of nonzero number
                      "2 this starts and ends with %", 0);
+#endif
 
     /* strftime() treats % with a number (and no specifier) as a literal string
      * to be formatted with a field width (undocumented and probably a bug ...)
      */
-    assert_hr_format("this ends with %10", "this ends with        %10",
+    assert_hr_format("this ends with %10",
+#ifdef HAVE_STRFTIME_EMPTY_SPEC_FAILS
+                     NULL, NULL, 0);
+#else
+                     "this ends with        %10",
                      // *BSD strftime() strips % in front of nonzero number
                      "this ends with 10", 0);
+#endif
 }
 
 static void
@@ -120,8 +139,20 @@ without_frac(void **state)
      * g_date_time_format() doesn't support field widths.
      */
     assert_hr_format("%3S seconds", "0" SECOND_S " seconds",
-                     // *BSD strftime() doesn't support field widths
+#if defined(HAVE_STRFTIME_WIDTH)
+                     NULL, 0);
+#elif defined(__FreeBSD__)
+                     /* FreeBSD doesn't support field width in strftime().  It
+                      * strips the leading % and copies the rest of the specifier
+                      * into the string.
+                      */
                      "3S seconds", 0);
+#else
+                     /* musl (and maybe other c libraries) ignores the field width
+                      * and handle the rest of the specifier normally.
+                      */
+                     SECOND_S " seconds", 0);
+#endif
 
     // strftime() treats %% as a literal %
     assert_hr_format("%%H %%N", "%H %N", NULL, 0);