diff --git a/Python/assemble.c b/Python/assemble.c
index b7012534d6cc4e..4f66cf294e38c9 100644
--- a/Python/assemble.c
+++ b/Python/assemble.c
@@ -18,7 +18,7 @@
 #define ERROR -1
 
 #define RETURN_IF_ERROR(X)  \
-    if ((X) == -1) {        \
+    if ((X) < 0) {          \
         return ERROR;       \
     }
 
@@ -448,13 +448,17 @@ static PyObject *
 dict_keys_inorder(PyObject *dict, Py_ssize_t offset)
 {
     PyObject *tuple, *k, *v;
-    Py_ssize_t i, pos = 0, size = PyDict_GET_SIZE(dict);
+    Py_ssize_t pos = 0, size = PyDict_GET_SIZE(dict);
 
     tuple = PyTuple_New(size);
     if (tuple == NULL)
         return NULL;
     while (PyDict_Next(dict, &pos, &k, &v)) {
-        i = PyLong_AS_LONG(v);
+        Py_ssize_t i = PyLong_AsSsize_t(v);
+        if (i == -1 && PyErr_Occurred()) {
+            Py_DECREF(tuple);
+            return NULL;
+        }
         assert((i - offset) < size);
         assert((i - offset) >= 0);
         PyTuple_SET_ITEM(tuple, i - offset, Py_NewRef(k));
@@ -466,24 +470,34 @@ dict_keys_inorder(PyObject *dict, Py_ssize_t offset)
 extern void _Py_set_localsplus_info(int, PyObject *, unsigned char,
                                    PyObject *, PyObject *);
 
-static void
+static int
 compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
                         PyObject *names, PyObject *kinds)
 {
     PyObject *k, *v;
     Py_ssize_t pos = 0;
     while (PyDict_Next(umd->u_varnames, &pos, &k, &v)) {
-        int offset = (int)PyLong_AS_LONG(v);
+        int offset = _PyLong_AsInt(v);
+        if (offset == -1 && PyErr_Occurred()) {
+            return ERROR;
+        }
         assert(offset >= 0);
         assert(offset < nlocalsplus);
+
         // For now we do not distinguish arg kinds.
         _PyLocals_Kind kind = CO_FAST_LOCAL;
-        if (PyDict_Contains(umd->u_fasthidden, k)) {
+        int has_key = PyDict_Contains(umd->u_fasthidden, k);
+        RETURN_IF_ERROR(has_key);
+        if (has_key) {
             kind |= CO_FAST_HIDDEN;
         }
-        if (PyDict_GetItem(umd->u_cellvars, k) != NULL) {
+
+        has_key = PyDict_Contains(umd->u_cellvars, k);
+        RETURN_IF_ERROR(has_key);
+        if (has_key) {
             kind |= CO_FAST_CELL;
         }
+
         _Py_set_localsplus_info(offset, k, kind, names, kinds);
     }
     int nlocals = (int)PyDict_GET_SIZE(umd->u_varnames);
@@ -492,12 +506,18 @@ compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
     int numdropped = 0;
     pos = 0;
     while (PyDict_Next(umd->u_cellvars, &pos, &k, &v)) {
-        if (PyDict_GetItem(umd->u_varnames, k) != NULL) {
+        int has_name = PyDict_Contains(umd->u_varnames, k);
+        RETURN_IF_ERROR(has_name);
+        if (has_name) {
             // Skip cells that are already covered by locals.
             numdropped += 1;
             continue;
         }
-        int offset = (int)PyLong_AS_LONG(v);
+
+        int offset = _PyLong_AsInt(v);
+        if (offset == -1 && PyErr_Occurred()) {
+            return ERROR;
+        }
         assert(offset >= 0);
         offset += nlocals - numdropped;
         assert(offset < nlocalsplus);
@@ -506,12 +526,16 @@ compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
 
     pos = 0;
     while (PyDict_Next(umd->u_freevars, &pos, &k, &v)) {
-        int offset = (int)PyLong_AS_LONG(v);
+        int offset = _PyLong_AsInt(v);
+        if (offset == -1 && PyErr_Occurred()) {
+            return ERROR;
+        }
         assert(offset >= 0);
         offset += nlocals - numdropped;
         assert(offset < nlocalsplus);
         _Py_set_localsplus_info(offset, k, CO_FAST_FREE, names, kinds);
     }
+    return SUCCESS;
 }
 
 static PyCodeObject *
@@ -556,7 +580,10 @@ makecode(_PyCompile_CodeUnitMetadata *umd, struct assembler *a, PyObject *const_
     if (localspluskinds == NULL) {
         goto error;
     }
-    compute_localsplus_info(umd, nlocalsplus, localsplusnames, localspluskinds);
+    if (compute_localsplus_info(umd, nlocalsplus,
+                                localsplusnames, localspluskinds) == ERROR) {
+        goto error;
+    }
 
     struct _PyCodeConstructor con = {
         .filename = filename,
diff --git a/Python/compile.c b/Python/compile.c
index 3260dba57eac8f..7418f509c87b14 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -4194,9 +4194,20 @@ compiler_nameop(struct compiler *c, location loc,
         optype = OP_DEREF;
         break;
     case LOCAL:
-        if (_PyST_IsFunctionLike(c->u->u_ste) ||
-                (PyDict_GetItem(c->u->u_metadata.u_fasthidden, mangled) == Py_True))
+        if (_PyST_IsFunctionLike(c->u->u_ste)) {
             optype = OP_FAST;
+        }
+        else {
+            PyObject *item;
+            if (PyDict_GetItemRef(c->u->u_metadata.u_fasthidden, mangled,
+                                  &item) < 0) {
+                goto error;
+            }
+            if (item == Py_True) {
+                optype = OP_FAST;
+            }
+            Py_XDECREF(item);
+        }
         break;
     case GLOBAL_IMPLICIT:
         if (_PyST_IsFunctionLike(c->u->u_ste))
@@ -4221,7 +4232,7 @@ compiler_nameop(struct compiler *c, location loc,
                 op = LOAD_FROM_DICT_OR_DEREF;
                 // First load the locals
                 if (codegen_addop_noarg(INSTR_SEQUENCE(c), LOAD_LOCALS, loc) < 0) {
-                    return ERROR;
+                    goto error;
                 }
             }
             else if (c->u->u_ste->ste_can_see_class_scope) {
@@ -4229,7 +4240,7 @@ compiler_nameop(struct compiler *c, location loc,
                 // First load the classdict
                 if (compiler_addop_o(c->u, loc, LOAD_DEREF,
                                      c->u->u_metadata.u_freevars, &_Py_ID(__classdict__)) < 0) {
-                    return ERROR;
+                    goto error;
                 }
             }
             else {
@@ -4256,7 +4267,7 @@ compiler_nameop(struct compiler *c, location loc,
                 // First load the classdict
                 if (compiler_addop_o(c->u, loc, LOAD_DEREF,
                                      c->u->u_metadata.u_freevars, &_Py_ID(__classdict__)) < 0) {
-                    return ERROR;
+                    goto error;
                 }
             } else {
                 op = LOAD_GLOBAL;
@@ -4290,6 +4301,10 @@ compiler_nameop(struct compiler *c, location loc,
         arg <<= 1;
     }
     return codegen_addop_i(INSTR_SEQUENCE(c), op, arg, loc);
+
+error:
+    Py_DECREF(mangled);
+    return ERROR;
 }
 
 static int
@@ -5518,8 +5533,13 @@ push_inlined_comprehension_state(struct compiler *c, location loc,
         if ((symbol & DEF_LOCAL && !(symbol & DEF_NONLOCAL)) || in_class_block) {
             if (!_PyST_IsFunctionLike(c->u->u_ste)) {
                 // non-function scope: override this name to use fast locals
-                PyObject *orig = PyDict_GetItem(c->u->u_metadata.u_fasthidden, k);
-                if (orig != Py_True) {
+                PyObject *orig;
+                if (PyDict_GetItemRef(c->u->u_metadata.u_fasthidden, k, &orig) < 0) {
+                    return ERROR;
+                }
+                int orig_is_true = (orig == Py_True);
+                Py_XDECREF(orig);
+                if (!orig_is_true) {
                     if (PyDict_SetItem(c->u->u_metadata.u_fasthidden, k, Py_True) < 0) {
                         return ERROR;
                     }
diff --git a/Python/flowgraph.c b/Python/flowgraph.c
index 719ed92105074e..e620e7cf1b9e96 100644
--- a/Python/flowgraph.c
+++ b/Python/flowgraph.c
@@ -2404,17 +2404,31 @@ build_cellfixedoffsets(_PyCompile_CodeUnitMetadata *umd)
     PyObject *varname, *cellindex;
     Py_ssize_t pos = 0;
     while (PyDict_Next(umd->u_cellvars, &pos, &varname, &cellindex)) {
-        PyObject *varindex = PyDict_GetItem(umd->u_varnames, varname);
-        if (varindex != NULL) {
-            assert(PyLong_AS_LONG(cellindex) < INT_MAX);
-            assert(PyLong_AS_LONG(varindex) < INT_MAX);
-            int oldindex = (int)PyLong_AS_LONG(cellindex);
-            int argoffset = (int)PyLong_AS_LONG(varindex);
-            fixed[oldindex] = argoffset;
+        PyObject *varindex;
+        if (PyDict_GetItemRef(umd->u_varnames, varname, &varindex) < 0) {
+            goto error;
+        }
+        if (varindex == NULL) {
+            continue;
+        }
+
+        int argoffset = _PyLong_AsInt(varindex);
+        Py_DECREF(varindex);
+        if (argoffset == -1 && PyErr_Occurred()) {
+            goto error;
         }
-    }
 
+        int oldindex = _PyLong_AsInt(cellindex);
+        if (oldindex == -1 && PyErr_Occurred()) {
+            goto error;
+        }
+        fixed[oldindex] = argoffset;
+    }
     return fixed;
+
+error:
+    PyMem_Free(fixed);
+    return NULL;
 }
 
 #define IS_GENERATOR(CF) \
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 9837e0f0d52e6d..8c321fbcfe4104 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -762,18 +762,30 @@ pycore_init_builtins(PyThreadState *tstate)
     }
     interp->builtins = Py_NewRef(builtins_dict);
 
-    PyObject *isinstance = PyDict_GetItem(builtins_dict, &_Py_ID(isinstance));
-    assert(isinstance);
+    PyObject *isinstance = PyDict_GetItemWithError(builtins_dict, &_Py_ID(isinstance));
+    if (!isinstance) {
+        goto error;
+    }
     interp->callable_cache.isinstance = isinstance;
-    PyObject *len = PyDict_GetItem(builtins_dict, &_Py_ID(len));
-    assert(len);
+
+    PyObject *len = PyDict_GetItemWithError(builtins_dict, &_Py_ID(len));
+    if (!len) {
+        goto error;
+    }
     interp->callable_cache.len = len;
+
     PyObject *list_append = _PyType_Lookup(&PyList_Type, &_Py_ID(append));
-    assert(list_append);
+    if (list_append == NULL) {
+        goto error;
+    }
     interp->callable_cache.list_append = list_append;
+
     PyObject *object__getattribute__ = _PyType_Lookup(&PyBaseObject_Type, &_Py_ID(__getattribute__));
-    assert(object__getattribute__);
+    if (object__getattribute__ == NULL) {
+        goto error;
+    }
     interp->callable_cache.object__getattribute__ = object__getattribute__;
+
     if (_PyBuiltins_AddExceptions(bimod) < 0) {
         return _PyStatus_ERR("failed to add exceptions to builtins");
     }