diff --git a/mypyc/lib-rt/vecs/librt_vecs.c b/mypyc/lib-rt/vecs/librt_vecs.c
index cad8cbfb23d2..023f1552588d 100644
--- a/mypyc/lib-rt/vecs/librt_vecs.c
+++ b/mypyc/lib-rt/vecs/librt_vecs.c
@@ -958,7 +958,19 @@ static PyTypeObject *get_vec_type(void) {
     return &VecType;
 }
 
+static int
+vecs_abi_version(void) {
+    return LIBRT_VECS_ABI_VERSION;
+}
+
+static int
+vecs_api_version(void) {
+    return LIBRT_VECS_API_VERSION;
+}
+
 static VecCapsule Capsule = {
+    vecs_abi_version,
+    vecs_api_version,
     &Vec_TAPI,
     &Vec_NestedAPI,
     &Vec_I64API,
diff --git a/mypyc/lib-rt/vecs/librt_vecs.h b/mypyc/lib-rt/vecs/librt_vecs.h
index d41cc7661482..b7700d4bd9f7 100644
--- a/mypyc/lib-rt/vecs/librt_vecs.h
+++ b/mypyc/lib-rt/vecs/librt_vecs.h
@@ -10,6 +10,16 @@
 #include <stdint.h>
 #include "mypyc_util.h"
 
+// ABI version -- only an exact match is compatible. This will only be changed in
+// very exceptional cases (likely never) due to strict backward compatibility
+// requirements.
+#define LIBRT_VECS_ABI_VERSION 1
+
+// API version -- more recent versions must maintain backward compatibility, i.e.
+// we can add new features but not remove or change existing features (unless
+// ABI version is changed, but see the comment above).
+#define LIBRT_VECS_API_VERSION 1
+
 #ifdef MYPYC_EXPERIMENTAL
 
 // Magic (native) integer return value on exception. Caller must also
@@ -500,6 +510,8 @@ typedef struct _VecNestedAPI {
 } VecNestedAPI;
 
 typedef struct {
+    int (*abi_version)(void);
+    int (*api_version)(void);
     VecTAPI *t;
     VecNestedAPI *nested;
     VecI64API *i64;
diff --git a/mypyc/lib-rt/vecs/librt_vecs_api.c b/mypyc/lib-rt/vecs/librt_vecs_api.c
index 7ac067ae4161..9993848f3a2e 100644
--- a/mypyc/lib-rt/vecs/librt_vecs_api.c
+++ b/mypyc/lib-rt/vecs/librt_vecs_api.c
@@ -28,9 +28,28 @@ import_librt_vecs(void)
     if (mod == NULL)
         return -1;
     Py_DECREF(mod);  // we import just for the side effect of making the below work.
-    VecApi = PyCapsule_Import("librt.vecs._C_API", 0);
-    if (!VecApi)
+    VecCapsule *capsule = PyCapsule_Import("librt.vecs._C_API", 0);
+    if (!capsule)
         return -1;
+    if (capsule->abi_version() != LIBRT_VECS_ABI_VERSION) {
+        char err[128];
+        snprintf(err, sizeof(err),
+                 "ABI version conflict for librt.vecs, expected %d, found %d",
+                 LIBRT_VECS_ABI_VERSION,
+                 capsule->abi_version());
+        PyErr_SetString(PyExc_ValueError, err);
+        return -1;
+    }
+    if (capsule->api_version() < LIBRT_VECS_API_VERSION) {
+        char err[128];
+        snprintf(err, sizeof(err),
+                 "API version conflict for librt.vecs, expected %d or newer, found %d (hint: upgrade librt)",
+                 LIBRT_VECS_API_VERSION,
+                 capsule->api_version());
+        PyErr_SetString(PyExc_ValueError, err);
+        return -1;
+    }
+    VecApi = capsule;
     VecI64Api = *VecApi->i64;
     VecI32Api = *VecApi->i32;
     VecI16Api = *VecApi->i16;