diff --git a/include/os_compat.h b/include/os_compat.h
index 3c87d01..df64c61 100644
--- a/include/os_compat.h
+++ b/include/os_compat.h
@@ -2,6 +2,7 @@
 #define CST_OS_COMPAT_H
 
 #include <stddef.h>
+#include <stdio.h>
 #include <time.h>
 
 #ifdef __cplusplus
@@ -12,6 +13,13 @@ extern "C" {
 #define OS_PATH_MAX 4096
 #endif
 
+/* --- text --- */
+/* One line of a file into *lineptr, growing it as needed: POSIX getline(3),
+ * which a MinGW CRT does not have (the session file readers used it directly
+ * and only the Windows build noticed). Returns the number of bytes read -- 0
+ * for an empty line -- or -1 at the end of the file. */
+long long os_getline(char **lineptr, size_t *n, FILE *stream);
+
 /* --- path --- */
 int os_path_is_abs(const char *p);
 /* Join with native separator; out always uses '/' on Unix and '\\' on Win for
diff --git a/src/os_compat.c b/src/os_compat.c
index b66fdbf..7a46401 100644
--- a/src/os_compat.c
+++ b/src/os_compat.c
@@ -1217,3 +1217,40 @@ int unsetenv(const char *name) {
 }
 
 #endif /* _WIN32 */
+
+/* getline(3) itself where the libc has it; the same thing spelled out with
+ * fgetc() where it does not (Windows), so the callers read the same on every
+ * platform. */
+long long os_getline(char **lineptr, size_t *n, FILE *stream) {
+#ifndef _WIN32
+  return (long long)getline(lineptr, n, stream);
+#else
+  if (!lineptr || !n || !stream)
+    return -1;
+  if (!*lineptr || *n == 0) {
+    *n = 256;
+    *lineptr = (char *)malloc(*n);
+    if (!*lineptr)
+      return -1;
+  }
+  size_t len = 0;
+  int c = 0;
+  while ((c = fgetc(stream)) != EOF) {
+    if (len + 2 > *n) {
+      const size_t nn = (*n) * 2;
+      char *nb = (char *)realloc(*lineptr, nn);
+      if (!nb)
+        return -1;
+      *lineptr = nb;
+      *n = nn;
+    }
+    (*lineptr)[len++] = (char)c;
+    if (c == '\n')
+      break;
+  }
+  if (len == 0 && c == EOF)
+    return -1;
+  (*lineptr)[len] = 0;
+  return (long long)len;
+#endif
+}
diff --git a/src/session.c b/src/session.c
index 5b0ede9..b6ae38a 100644
--- a/src/session.c
+++ b/src/session.c
@@ -15,39 +15,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef _WIN32
-typedef long long cst_ssize_t;
-static cst_ssize_t cst_getline(char **lineptr, size_t *n, FILE *stream) {
-  if (!lineptr || !n || !stream)
-    return -1;
-  if (!*lineptr || *n == 0) {
-    *n = 256;
-    *lineptr = (char *)malloc(*n);
-    if (!*lineptr)
-      return -1;
-  }
-  size_t len = 0;
-  int c = 0;
-  while ((c = fgetc(stream)) != EOF) {
-    if (len + 2 > *n) {
-      size_t nn = (*n) * 2;
-      char *nb = (char *)realloc(*lineptr, nn);
-      if (!nb)
-        return -1;
-      *lineptr = nb;
-      *n = nn;
-    }
-    (*lineptr)[len++] = (char)c;
-    if (c == '\n')
-      break;
-  }
-  if (len == 0 && c == EOF)
-    return -1;
-  (*lineptr)[len] = 0;
-  return (cst_ssize_t)len;
-}
-#define getline cst_getline
-#endif
+#include "os_compat.h"
 
 struct cst_session {
   char path[4096];
@@ -158,7 +126,7 @@ static void load_existing(cst_session_t *s) {
     return;
   char *line = NULL;
   size_t cap = 0;
-  while (getline(&line, &cap, rp) != -1) {
+  while (os_getline(&line, &cap, rp) != -1) {
     cJSON *o = cJSON_Parse(line);
     if (!o || !cJSON_IsObject(o)) {
       cJSON_Delete(o);
diff --git a/src/tools/session_tools.c b/src/tools/session_tools.c
index 2c42556..df1ff9b 100644
--- a/src/tools/session_tools.c
+++ b/src/tools/session_tools.c
@@ -121,8 +121,8 @@ int cst_tool_session_search(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
     char *line = NULL;
     size_t cap = 0;
     cst_buf_t one = {0};
-    ssize_t got;
-    while ((got = getline(&line, &cap, fp)) > 0) {
+    long long got;
+    while ((got = os_getline(&line, &cap, fp)) > 0) {
       lineno++;
       scanned_bytes += got;
       /* A tool output line can be megabytes (a whole file read back): such a