diff --git a/src/pipeline/pass_definitions.c b/src/pipeline/pass_definitions.c
index b83cf5b80..676f1b169 100644
--- a/src/pipeline/pass_definitions.c
+++ b/src/pipeline/pass_definitions.c
@@ -103,7 +103,9 @@ static int def_json_escape_char(char *buf, size_t avail, char ch) {
         break;
     default:
         if (avail >= SKIP_ONE) {
-            buf[0] = ch;
+            /* Any other raw control byte (e.g. form feed) is invalid inside a
+             * JSON string — degrade to a space. */
+            buf[0] = ((unsigned char)ch < 0x20) ? ' ' : ch;
         }
         return SKIP_ONE;
     }
@@ -194,14 +196,11 @@ static void append_json_str_array(char *buf, size_t bufsize, size_t *pos, const
         if (p < bufsize - SKIP_ONE) {
             buf[p++] = '"';
         }
+        /* Full escaping (not just quote/backslash): items like C param types
+         * sliced from multi-line declarations carry raw \n/\t bytes, which are
+         * invalid inside JSON strings. */
         for (const char *s = arr[i]; *s && p < bufsize - PD_ESC_SPACE; s++) {
-            if (*s == '"' || *s == '\\') {
-                buf[p++] = '\\';
-                if (p >= bufsize - PD_ESC_SPACE) {
-                    break;
-                }
-            }
-            buf[p++] = *s;
+            p += (size_t)def_json_escape_char(buf + p, bufsize - p - PD_ESC_SPACE, *s);
         }
         if (p < bufsize - SKIP_ONE) {
             buf[p++] = '"';
diff --git a/src/pipeline/pass_parallel.c b/src/pipeline/pass_parallel.c
index 4713b77c6..91dd5601f 100644
--- a/src/pipeline/pass_parallel.c
+++ b/src/pipeline/pass_parallel.c
@@ -145,7 +145,9 @@ static int json_escape_char(char *buf, size_t avail, char ch) {
         break;
     default:
         if (avail >= SKIP_ONE) {
-            buf[0] = ch;
+            /* Any other raw control byte (e.g. form feed) is invalid inside a
+             * JSON string — degrade to a space. */
+            buf[0] = ((unsigned char)ch < 0x20) ? ' ' : ch;
         }
         return SKIP_ONE;
     }
@@ -237,14 +239,11 @@ static void append_json_str_array(char *buf, size_t bufsize, size_t *pos, const
         if (p < bufsize - SKIP_ONE) {
             buf[p++] = '"';
         }
+        /* Full escaping (not just quote/backslash): items like C param types
+         * sliced from multi-line declarations carry raw \n/\t bytes, which are
+         * invalid inside JSON strings. */
         for (const char *s = arr[i]; *s && p < bufsize - PP_ESC_SPACE; s++) {
-            if (*s == '"' || *s == '\\') {
-                buf[p++] = '\\';
-                if (p >= bufsize - PP_ESC_SPACE) {
-                    break;
-                }
-            }
-            buf[p++] = *s;
+            p += (size_t)json_escape_char(buf + p, bufsize - p - PP_ESC_SPACE, *s);
         }
         if (p < bufsize - SKIP_ONE) {
             buf[p++] = '"';
diff --git a/tests/test_pipeline.c b/tests/test_pipeline.c
index d2ed468fd..333865229 100644
--- a/tests/test_pipeline.c
+++ b/tests/test_pipeline.c
@@ -506,6 +506,23 @@ TEST(pipeline_def_props_valid_json_when_oversized) {
         fclose(f);
     }
 
+    /* Multi-line parameter declarations: param_types items then carry raw
+     * newline/tab bytes from the source slice. The array appender's inline
+     * escape loop only handled quote/backslash, so the raw control bytes made
+     * the JSON invalid (118 Linux-kernel rows of this shape). */
+    {
+        char path[512];
+        snprintf(path, sizeof(path), "%s/sweep_nl.c", g_tmpdir);
+        FILE *f = fopen(path, "w");
+        if (!f) {
+            teardown_test_repo();
+            FAIL("failed to write sweep_nl.c");
+        }
+        fprintf(f, "int sweep_fn_nl(struct\n\t\t\t\treally_long_struct_name *a,\n"
+                   "          enum\n\tweird_enum b) { return 0; }\n");
+        fclose(f);
+    }
+
     char db_path[512];
     snprintf(db_path, sizeof(db_path), "%s/test_huge_props.db", g_tmpdir);
     cbm_pipeline_t *p = cbm_pipeline_new(g_tmpdir, db_path, CBM_MODE_FULL);
@@ -539,7 +556,7 @@ TEST(pipeline_def_props_valid_json_when_oversized) {
         yyjson_doc_free(doc);
         checked++;
     }
-    ASSERT_EQ(checked, 60); /* all sweep functions present */
+    ASSERT_EQ(checked, 61); /* all sweep functions present (60 sizes + nl case) */
 
     cbm_store_free_nodes(funcs, func_count);
     cbm_store_close(s);